Unraveling the Efficacy of Differentiated Instruction in Enhancing Second Language Acquisition: A Comprehensive Review and Future Directions

| ABSTRACT "The art of teaching is the art of assisting discovery," as famously quoted by Mark Van Doren, epitomizes the philosophy of Differentiated Instruction (DI). This teaching strategy modifies lessons and learning environments to meet students' diverse learning needs, interests


Introduction
Language is a central communication tool in fostering social interaction and cultural understanding. The ability to master a second language (L2) is not just an asset but a necessity in today's globalized world. Second Language Acquisition (SLA) has drawn considerable attention from researchers and educators in recent decades, who have strived to unearth effective strategies and methodologies to enhance language learning. One such approach that has gained traction is Differentiated Instruction (DI), a pedagogical method that tailors teaching and learning to meet individual learners' needs. The importance of DI stems from the heterogeneous nature of classrooms, particularly with the rising multiculturalism in schools and institutions worldwide. The core of differentiated instruction lies in adapting teaching techniques, educational materials, and learning content to cater to individual learners' learning needs, abilities, and interests (Tomlinson, 2001). Differentiated instruction practice starkly contrasts the traditional 'one-size-fits-all' teaching modal, offering a more tailored, flexible framework that ensures all students can effectively engage with the study materials. Differentiated instruction takes on an added layer of importance within second language learning.

Process:
The differentiation process in education focuses on how students learn and understand the content. It involves utilizing various activities, strategies, and methods to support students in comprehending and internalizing knowledge. These approaches include collaborative learning, direct instruction, problem-solving tasks, research projects, and creative assignments. Selecting specific strategies depends on students' readiness, learning styles, and interests. By adapting the learning process to meet individual needs, teachers can establish a supportive and engaging environment for students (Tomlinson & Imbeau, 2010).
Extensive research has consistently demonstrated the positive impact of differentiated instructional strategies on student engagement, motivation, and overall learning outcomes. For instance, a study by Tomlinson (1999) revealed that implementing differentiated mathematics instruction increased student motivation and achievement. Similarly, Douglas (2019) found that incorporating differentiated instruction in a foreign language classroom increased student engagement and improved language proficiency. These findings reinforce the effectiveness of differentiation practices in enhancing the learning process.
Product: Assessment differentiation offers students various options for demonstrating their understanding and skills beyond traditional written exams. This approach allows students to showcase their learning through multiple products, such as oral presentations, creative projects, and multimedia creations. By providing multiple pathways for assessment, educators cater to student's unique strengths and interests, promoting engagement and increasing their sense of ownership in the learning process. Assessment differentiation recognizes that students have different ways of expressing their knowledge and abilities, promoting inclusivity and enhancing the accuracy of evaluating their performance. (Tomlinson & Imbeau, 2010). This instructional approach expands beyond traditional written exams by offering students a variety of assessment methods, including oral presentations, creative projects, and multimedia creations, to leverage their strengths and interests, fostering increased engagement and enhanced learning outcomes. The integration of differentiated instruction and assessment practices facilitates the creation of inclusive learning environments that cater to the diverse needs of students, thereby promoting their growth and achievement. Empirical evidence substantiates the advantages of differentiated assessments. For instance,  reported that providing multiple avenues for demonstrating understanding significantly improved student motivation and overall performance.
Similarly, Fairbairn and Jones-Vo (2010) underscored the positive impact of differentiated assessments on student self-efficacy and their sense of ownership in the learning process. These findings emphasize the significance of incorporating diverse product options during assessments, enabling students to demonstrate their knowledge and skills in alignment with their abilities and preferences. Moreover, employing differentiated grading and marking approaches corresponding to the various product choices promotes fairness and accuracy in evaluating student performance.
Learning Environment: The learning environment is critical when implementing differentiation in the classroom (Tomlinson & Imbeau, 2010). It encompasses the physical space, classroom culture, and atmosphere. To support the diverse needs of students, teachers must create an environment that is safe, supportive, and inclusive. This includes designing individual and collaborative workspaces, establishing class norms that promote respect and collaboration, and fostering a positive and accepting classroom climate. Research has consistently shown that a well-structured learning environment significantly impacts student motivation, engagement, and learning outcomes. Educators can promote inclusion, enhance student engagement, and facilitate effective learning for all students by consciously designing the learning environment to cater to diverse learners. This might involve creating spaces for individual work, group work, and direct instruction or setting class norms that promote respect and collaboration (Tomlinson & Imbeau, 2010). A well-structured learning environment can boost motivation, engagement, and learning outcomes. The emphasis on the four critical elements of the process, content, product, and learning environment has garnered attention from various scholars and researchers in the field (Bidari, 2021; Fairbairn & Jones-Vo, 2010; Tomlinson & Imbeau, 2010). Educators can create inclusive and engaging learning environments that cater to student's diverse needs, abilities, and interests by prioritizing differentiation in these areas. Tomlinson's work underscores the importance of addressing student diversity, promoting inclusion, fostering student engagement, and facilitating effective student learning outcomes.

Differentiated Instruction and L2 Development
The literature on differentiated instruction in ESL and EFL contexts is extensive and diverse. According to the theoretical frameworks of Tomlinson's DI model (2001), adapting instruction to individual learners' needs can improve understanding and skill acquisition. Several studies have investigated DI in the context of language learning. For example, Suprayogi (2017) and Rock et al. (2018) revealed improved student outcomes when DI was used in EFL courses. Furthermore, the role of instructors' opinions on DI practice implementation has been highlighted (Deunk, 2018& Subban, 2006. Most teachers have a generally positive perception of DI, acknowledging its potential to enhance student engagement, participation, and learning outcomes. Teachers play a crucial role in implementing differentiated instruction. Their understanding, beliefs, and attitudes toward DI significantly influence its effective implementation. Research has shown that teachers perceive differentiated instruction in second-language classrooms as beneficial for students' language development and overall learning experience (Tomlinson, 2017). According to a study by Gorman and Martin (2020), teachers perceive DI to address students' diverse linguistic and cultural backgrounds, allowing them to tailor instruction to individual needs and maximize learning outcomes. However, a considerable minority express concerns about the practicality of implementing DI due to large class sizes, diverse student needs, and limited resources. In a study by Hornberg and Sandberg (2021), teachers expressed concerns about managing classroom dynamics and maintaining an inclusive learning environment while providing differentiated instruction. Teachers also highlighted the need for additional resources, training, and support to effectively implement DI strategies (Freeman & Mercuri, 2017).

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Gregory and Chapman (2013) examined the application of DI in L2 development. The authors highlight the benefits of DI in English as a Second Language (ESL) classrooms. They argue that teachers can more effectively support language acquisition by tailoring instruction to meet individual needs. Reis et al. (2011) further studied the role of DI in promoting academic achievement among ESL students. They found that students in differentiated classrooms showed significantly better progress in language acquisition than their counterparts in traditional classrooms. This was attributed to the personalized approach of DI, which allows students to engage with materials at their own pace and level.  found that differentiated instruction improved learners' language proficiency, particularly in their listening and speaking skills. Demirel and Dağyar (2016) found that DI significantly increased secondlanguage learners' reading and writing skills. Students' perceptions of differentiated instruction in second-language classrooms can substantially impact their engagement, motivation, and language learning outcomes. Students perceive differentiated instruction as a positive and inclusive approach that values their strengths and needs (Tomlinson, 2017). Students appreciate the opportunity to learn at their own pace, receive personalized feedback, and engage in activities that align with their interests and learning styles (Gorman & Martin, 2020). Furthermore, differentiated instruction promotes a sense of autonomy and ownership among students, fostering their self-esteem and confidence in language learning.
A study by Solano-Flores (2016) found that students valued the individual attention and support provided through differentiated instruction, leading to increased motivation and language proficiency. DI in second-language classrooms recognizes individual student differences by adjusting and customizing the educational process to meet the requirements of varied learners. Meeting each student's individual learning needs and supporting their progress aims to optimize each learner's growth and personal achievement (Tomlinson, 2001). Differentiation can occur via content, method, product, or learning environment, depending on students' preparedness, interest, or learning profiles (Tomlinson & Imbeau, 2010). For example, in terms of content, teachers may supply materials at various reading levels to accommodate students' differing degrees of language skill. DI is especially crucial in the formation of second languages. Learners vary in language competency, cultural background, and learning style. Effectively tailored instruction can help accommodate these variances, enhancing language learning success (Gibbons, 2002).
Huang and Yao (2020) discovered that differentiated teaching significantly enhanced second language learners' overall academic performance in a meta-analysis. The study also found that DI was more effective for students with lower skill levels, implying that this strategy might aid in closing the achievement gap in second language acquisition. However, adopting DI in the classroom might be difficult. Teachers must assess students' specific requirements, provide suitable learning activities, and manage many learning processes simultaneously. Professional growth and collaborative planning can benefit teachers applying DI (Levy, 2008). In Bidar's (2021) study, teachers generally have positive attitudes toward differentiated instruction but face several challenges in implementing it effectively, such as a lack of resources and training. Hence, professional development opportunities and support from school administrators can help overcome these challenges. In addition, teachers may face challenges in managing the different needs of learners and providing appropriate feedback (Tomlinson, 2014). These challenges may be particularly acute in most classrooms where resources and training opportunities may be limited. Differentiated Instruction is critical for second language growth. DI can assist students in enhancing their language learning outcomes by adjusting learners' specific needs and features. Despite the potential benefits of DI, there are several challenges associated with its implementation. One of the main challenges is a lack of teacher training and resources. Teachers may not have the necessary skills and knowledge to effectively implement DI in their classrooms (Tomlinson, 2014).

Benefits of (DI)
This section presents the benefits of differentiated instruction in second language learning from the reviewed literature. It emphasizes the potential of DI in enhancing L2 learning outcomes, promoting learner engagement, improving students' motivation and self-efficacy, promoting inclusive education, and more. However, it also highlights challenges such as the increased teacher workload, the need for professional development to implement DI effectively, and the need for quantitative research validating the long-term positive impacts of DI in SLA. In the current educational landscape, teachers are often burdened with multiple responsibilities, including preparing students for high-stakes testing and ensuring the survival of their schools. This pressure can lead to a focus on test-oriented teaching rather than a more holistic, knowledge-centered approach (Uddin, 2019).
However, it is crucial to recognize the importance of incorporating differentiating pedagogy as a vital teaching strategy. Differentiating pedagogy empowers learners by tailoring instruction to meet their diverse needs and interests while fostering their knowledge and understanding. By integrating differentiating pedagogy into the classroom, teachers can create a transformative learning environment that prepares students for assessments, nurtures their strengths, promotes inclusivity, and enhances their learning experience. It is essential to prioritize the balance between test-oriented teaching and a broader, knowledge-centered approach that embraces differentiating pedagogy, ultimately empowering students to become engaged and successful learners.
Here are some key reasons why differentiated instruction is vital for students' language development.
Promotes Inclusive Learning and Enhances Comprehension: Differentiated instruction supports diverse learners, including those with varying language proficiency levels. Differentiated instruction ensures that all students can participate in classroom activities and learn effectively by meeting students where they are. According to Tomlinson (2001), "Differentiation is a philosophy, a way of thinking about teaching and learning. It means ensuring that every student grows and learns" (p. 15). By differentiating content, process, and product, teachers can better match instruction to each student's level of understanding, thereby enhancing comprehension. Tomlinson & Allan (2000) posit that "difference implies an ongoing, flexible approach that allows for in-themoment modification of lesson plans and teaching approaches, to make instruction more responsive to learner needs and promote greater understanding" (p. 8).

Supports Multiple Modes of Expression and
Learning Pace: Differentiated instruction allows students to express their understanding in various ways, which can be particularly beneficial for language learners. As Gardner's (1983) Multiple Intelligences Theory suggests, providing varied modes of expression allows students to leverage their strengths, which can, in turn, foster language development. Differentiated instruction accommodates each student's pace of learning, which is particularly important for language development. Some students may need more time to understand and practice language skills, while others may advance more quickly. Tomlinson (2001) argues that "a 'one-size-fits-all' approach to schooling... is ill-suited to our goal of helping all students develop the skills and knowledge they will require for the future" (p. 32).

Addresses Diverse Learning Needs and Active Engagement:
Students come from diverse linguistic backgrounds, and their language skills may vary widely. Differentiated instruction allows educators to tailor lessons to meet these changing needs, ensuring that all students can develop their language skills effectively. "Students' readiness levels, interests, and learning profile characteristics are considered in the planning and implementation of instruction" (Tomlinson & McTighe, 2006, p. 3). Differentiated instruction often includes various engaging activities designed to meet diverse learning preferences. This active engagement can enhance motivation and ultimately boost language acquisition. Lightbown & Spada (2013) noted that "learner engagement is crucial to effective second language acquisition." As Peregoy and Boyle (2013) argue, engagement can significantly improve language development: "When students are motivated and actively engaged, they take more ownership of their learning and are likely to make more significant progress" (p. 126). Language learning requires ample practice. Differentiated instruction can provide opportunities for meaningful practice tailored to each student's level, enhancing their language skills and fluency. As Krashen (1982) posited, providing comprehensible input beyond the learner's current language proficiency promotes language acquisition.
Facilitates Peer Learning and Self-Directed Learning: Differentiated instruction often includes collaborative activities, which provide opportunities for peer learning. This can be particularly beneficial for language development, allowing students to learn from each other's linguistic skills and perspectives. According to Vygotsky's (1978) sociocultural learning theory, peer interaction plays a crucial role in language learning. By providing diverse options and resources, differentiated instruction can encourage selfdirected learning, fostering autonomy and motivation in language learning. Holec (1981) notes that learner autonomy is crucial to successful language learning. Hence, differentiated instruction plays a pivotal role in language development. Catering to diverse learning needs, promoting active engagement, providing meaningful practice, facilitating peer learning, and encouraging selfdirected learning enables all students to develop their language skills effectively. While differentiated instruction requires thoughtful planning and implementation, its benefits for language development make it an invaluable approach in today's diverse classrooms. As Tomlinson (2001) stated, "The idea of differentiating instruction is an approach to teaching that advocates active planning for and attention to student differences in classrooms in the context of high-quality curriculums." This underscores the necessity of differentiation to ensure all students succeed in their language development journey.

Differentiated Instruction Strategies
Incorporating differentiation practices in the classroom requires planning, flexibility, and a deep understanding of students' individual learning needs. Here is a closer look at how teachers can effectively implement differentiation strategies to meet students` diverse learning needs and create an inclusive classroom environment.

Understanding Student Readiness and Interests:
The first step to differentiation is understanding each student's readiness, learning profile, and interests. Teachers can use various assessment tools and strategies, including quizzes, class discussions, observation, and self-assessments, to gauge students' prior knowledge, skill levels, and learning styles. They can also gather information about students' interests and hobbies, which can be used to make lessons more engaging. Differentiating Content, Process, and Product: Teachers can begin to differentiate content once they understand their students' readiness and interest. This might involve providing the same content at different complexity levels, offering different resources (e.g., texts, videos, interactive online resources), or adjusting the pace of instruction. For instance, a teacher could provide reading materials at different levels to cater to students with varying reading abilities. Teachers can also differentiate the process or

Unraveling the Efficacy of Differentiated Instruction in Enhancing Second Language Acquisition: A Comprehensive Review and Future Directions
Page | 80 activities students engage in to learn the content. This might involve using varied teaching strategies such as direct instruction, cooperative learning, inquiry-based learning, or problem-based learning. Teachers can group students flexibly based on their readiness, interest, or learning profile, ensuring that each student is appropriately challenged and supported. Differentiating product means giving students different ways to demonstrate their understanding. For instance, a teacher might allow some students to write a report while others make a presentation, create a poster, or even produce a short video. This approach allows students to work in their preferred medium, leading to greater engagement and deeper understanding.
Creating a Supportive Learning Environment: Teachers can cultivate a supportive and accepting learning environment. This involves creating classroom norms that respect individual differences and promote collaboration. It might also include adjusting the physical environment-for instance, creating spaces for group work, individual work, and direct instruction. In addition, teachers can also ensure that all students are valued by acknowledging and celebrating their achievements, interests, and cultural backgrounds.

Continuous Assessment and Adjustment:
Differentiation is not a one-time event but an ongoing process. Teachers should continually assess student progress and adjust their instruction as needed. This might involve changing group compositions, providing additional support or challenge, or even rethinking their approach. Teachers can ensure that they always meet their students' changing needs by continually assessing and adjusting. The use of formative assessments as a tool to measure student understanding in real time is another crucial approach that teachers can incorporate in their classrooms. These assessments can be as formal as a quiz or as informal as an exit ticket, where students write down something they learned during the lesson. These assessments provide immediate feedback to the teacher about what the students understand and where there might be gaps. Teachers can then use this information to adjust their instruction and provide additional support where needed.
Leveraging Technology and Incorporating Student Choice: Technology offers many tools for differentiation. Digital learning platforms can provide content at different levels, offer various ways for students to engage with the material, and even provide additional avenues for demonstrating understanding. Additionally, assistive technologies can be invaluable in supporting students with special needs. However, ensuring all students have access to the necessary technology and understand how to use it is essential. Giving students a choice in their learning can significantly increase engagement. This could be a choice of topic, how they engage with the material (e.g., reading a text vs. watching a video), or how they demonstrate their understanding. Choice can be particularly effective when it allows students to connect learning to their personal interests or real-world issues.
Differentiating Homework and Assignments: Homework and assignments can also be differentiated to meet students' needs better. This might involve providing different task options, allowing students to work at their own pace, or adjusting the difficulty level of assignments. For instance, for a research project, you provide more structure and guidance for struggling students while offering advanced students more independence and challenge.
Providing Ongoing Feedback: Feedback is a critical component of the learning process. Regular, constructive feedback helps students understand their strengths and weaknesses and guides them toward improvement. Feedback can be provided in various forms, such as written comments, one-on-one discussions, or peer feedback. Teachers can make learning more relevant, engaging, and effective for each student by differentiating content, process, product, and learning environment. It is important to remember that differentiation is not about creating individual lesson plans for each student but about being responsive to student's needs, strengths, and interests. By incorporating these strategies, teachers can create an inclusive learning experience that maximizes each student's potential. This comprehensive review highlight that differentiated instruction is crucial in providing quality education by addressing diverse learning needs. It promotes active engagement, meaningful practice, peer learning, and selfdirected learning, challenging traditional teaching models. Tomlinson (2001) added that differentiated instruction is an approach that involves planning and attending to student differences within high-quality curriculums. This review emphasizes the necessity of systemic changes in educational practices to ensure that all students can excel in their second language development. Adopting dynamic, student-centered teaching strategies becomes essential, especially in increasingly diverse classrooms.
The discussion emphasizes the significance of differentiated instruction in language development and its implications for educational practices, policies, teacher education programs, and research. As highlighted by Uddin (2019), it is crucial to provide examples of how teachers utilize critical strategies in the classroom, positively influencing student thinking and learning. This underscores the pivotal role of differentiated instruction in promoting language development, particularly in diverse classrooms. The implications of differentiated instruction extend beyond the school, influencing educational practices, policies, teacher education programs, and research. The review findings contend that differentiated instruction is essential for effective teaching and learning, particularly in second language development. It emphasizes the importance of educators and policymakers embracing the DI approach to foster inclusive and high-quality education for all students. The research highlights the need for further exploration and implementation of differentiated instruction strategies to enhance language learning outcomes and meet the diverse needs of learners in today's classrooms.

Conclusion and Implications
This review article underscores the need for educators to embrace differentiated instruction, considering it not just as an optional teaching strategy but as an integral approach to meeting diverse student needs. This literature review suggests the need for professional development programs that equip teachers with the knowledge and skills to implement differentiated instruction effectively. Educational policies should be designed to support differentiated instruction. This could include smaller class sizes, making differentiated instruction more manageable, encouraging aging curriculum flexibility, and enabling teachers to tailor content, process, product, and the learning environment to meet diverse student needs. Implications also extend to teacher education programs. These programs should incorporate differentiated instruction into their curriculum, ensuring that aspiring teachers are well-equipped to cater to diverse classrooms. In-service training and professional development opportunities can help current educators enhance their differentiated instruction techniques.
Additionally, the review implies the need for proper resource allocation. Differentiated instruction may require various resources, including diverse learning materials and technologies. School administrators and policymakers should consider these needs when planning budgets and resources. The review also has implications for educational research. While the review points to the benefits of differentiated instruction, more research may be needed to understand its effectiveness in different contexts and with different student populations. The need for further research is evident, particularly in DI barriers. The aim would be to explore ways to mitigate these challenges, helping to facilitate the practical application of DI in second-language classrooms. For instance, the research could focus on using technology to save teachers' planning time or how to assess students in a differentiated classroom effectively. Moreover, longitudinal studies examining the long-term effects of DI on students' language development and overall academic achievement could provide valuable insights into the future of DI in ESL/EFL education.
Funding: This research received no external funding.