Each individual is unique and different from others. They have different learning, perceiving and understanding capacity. They are different from each other in terms of both their physical characteristics and cognitive, affective, psychomotor and moral characteristics. Some of them are good at sport, some of them at art, some of them at using words, and some good at making other happy. Each student has different interests and learning style as a result of her/his habits and brain functions. The students who watch the same movie  can  make  different deductions. Some of us see the glass half empty while some of us see the glass half full. We should accept the world in which each individual is different from each other (Kurt and Ekici, 2013; Özden, 2014; Tomlinson, 2014).

Several factors like the multiculturalism’s becoming prevelant, student differences, new studies conducted on learning and rapid social changes makes it necessary that teaching strategies should be changed (Gregory and Chapman, 2007). Even though everyone accepts that all students are different from each other, this assumption  is not included in the school system. The problem of not including the individual learning styles and differences in the curriculum is left to the discretion of the teachers. Hence, the teachers are to reorganize the curriculum according to the capacities, interests and learning pace of the students by differentiating them from each other (Kapusnick and Hauslein, 2001). Therefore, it is quite important that while designing teaching and learning environments, individual characteristics of the students should be considered for an effective teaching. These differences should not be ignored and they should be transformed into advantages for an effective teaching (Tomlinson, 2005).

Interests, attitudes, learning styles, readiness in terms of individual differences and the intelligence, abilities and creativeness of the students should be considered while preparing curriculums. It is seen that many prepared curriculums are intended for the individuals who have normal-level intelligence (Gökdere, 2004). They should be neither very hard nor very easy and not be for an average student same as before but they should be prepared according to the individual differences of the students (ÇalıkoÄŸlu, 2014). Expecting a curriculum which is prepared for the middle-level students can appeal that all the students should not be right. In today’s education environments, the teachers should know how to respond to the students with these individual differences (Subban, 2006).

The pedagogues have been arguing about a curriculum which can meet all the needs of the students with individual differences. The conducted studies revealed that the most effective curriculum about this subject is differentiated instruction (Bailey and Williams-Black, 2008). A differentiated classroom should answer all the special needs of all the students. Differentiated instruction presents various options to the students who aim success. It presents appropriate options to the students for active success. The teachers differentiate the content, evaluation tools, performance assignments and teaching strategies considering the needs of the students (Gregory and Chapman, 2007).

Differentiated instruction is an approach which responds to differences of the students in the same classroom like their needs, readiness, former learnings and learning styles. It is a process through which each student reaches the highest standards they can (Hall, 2002; Anderson, 2007). Differentiated instruction includes educational practices and strategies that provide the students including the disabled ones to be successful in the general educational environments and it provides the best educational presciption for all the students (Santamaria and Thousand, 2004).

Organizing an educational environment that is appropriate to the needs and levels of the students is in the responsibility of the school, and the students cannot be expected to adapt a  school  environment  which  does not respond to their own needs (Tomlinson, 2005). If an individual is not educated according to his/her needs, these individuals may lose their abilities or their abilities can be directed to other areas (Yaman, 2014). Thus, the teachers should vary the education according to the characteristics of the students and the content, process, products, emotions and educational environment should be designed as they can respond to the individual needs of different students (Avcı and Yüksel, 2014).

A differentiated classroom provides different activities which help the students learn the content, process their ideas and legitimate them and develop products which ensure effective learning (Tomlinson, 2015). In differentiated instruction, the teachers consider the readiness levels of the students rather than the curriculum. The teachers present the students different learning models by considering their individual differences. To do so, they diversify the teaching by considering the interests, talents, learning style and learning pace of the students (Tomlinson, 2014).

An important group of students who are neglected with the idea that “they already know” is the individuals with superior intelligence. Even though they have perfectionist standards from their early ages, they always need help for these needs (DaÄŸlıoÄŸlu, 2004). As the normal educational environments would have a restraining effect on the education of the individual with superior intelligence, they cannot be sufficient for these students. It is as important to give correct education in correct places as discovering the individuals with superior intelligence on time. The individuals with superior intelligence need unique curriculum, software and program to strengthen their abilities. The studies which have been conducted for years show that different curriculums are needed in the education of the individuals who have special talents. If the individuals with special talents are not educated in the direction of their needs, these individuals can lose their special talents or direct them to different fields (Yaman, 2014). The conducted studies show that the classrooms which include differentiated curriculums are the effective educational environments for the individuals with special talents (Yaman, 2014; ÇalıkoÄŸlu, 2014; Chen, 2011; Karaduman, 2012; Kök, 2012). With its focus on individual differences and effective methods, differentiated instruction has considerably changed the success, attitudes of not only the individuals with special talents but also the students in the normal classes in a positive way (YabaÅŸ, 2008; KaradaÄŸ, 2010; Demir, 2013).

The dissertations constitute another dimension of the conducted studies related to differentiated instruction. On analyzing the literature, it is seen that the interpretations related to the subject are inadequate. This study will provide an evaluation of the dissertations about differentiated instructions from various aspects by developing a holistic perspective. With this respect, it is thought that it will be a source for the future studies to be conducted about differentiated instruction.

The purpose of the study

The purpose of this study is to analyze the dissertations about differentiated instruction in terms of their contents with content analysis. Answers to the questions below are sought in the direction of this purpose.

1. How are the dissertations about the differentiated instruction in Turkey distributed in terms of year and type?

2. Which fields are the dissertations about the differentiated instruction in Turkey conducted on?

3. What are the themes of the dissertations about the differentiated instruction in Turkey?

4. What are the research models of the dissertations about the differentiated instruction in Turkey?

5. What are the data collection tools of the dissertations about the differentiated instruction in Turkey?

6. Who are the research staffs of the dissertations about the differentiated instruction in Turkey? 

In this section, information about the research model, data collection, data analysis and the limitedness of the study is presented.

The research model

This study is a qualitative research. Qualitative research is a method in which qualitative data collection tools like interview, observation and document analysis are used, and the facts and perceptions are presented in their natural environment (Yıldırım and ÅžimÅŸek, 2013). It provides to present complication in a rich and holistic content (Miles and Huberman, 2015). Document review that is commonly used in the qualitative research was used as a data collection tool. Document review is analysing of the materials that is related with the research topic. These documents can be journals book, pictures, pictures, movie and also daily (Cansız, 2014).  In this sense, it is aimed in this study to evaluate the dissertations about differentiated instruction with a holistic perspective using document analysis in this study. The dissertations are analyzed in terms of method, theme, interests, research staff, distributions by years and data collection tools.

Data collection

This study aims to analyze the dissertations about differentiated instruction in Tukey. In this direction, the dissertations collected from Council of Higher Education National Thesis Center database constitute the scope of this study. The manuscripts of the dissertations have been reached by using the key words “differentiated instruction.” On analyzing the database of Council of Higher Education without year limitation, 19 dissertations about differentiated instruction have been found. Three of these dissertations are limited to access. On analyzing the abstracts of the dissertations limited to access, it has been seen that if these dissertations were not included in the study, there would be no data loss and it is decided not to include them in the study. So, the study has been conducted with 19 dissertations about differentiated instruction.

Data analysis

The data obtained from the dissertations were analyzed with descriptive analysis. The data that gathered in the descriptive analysis is summarized and explained. Data is organized according to the research questions (Yıldırım and Şimşek, 2013). In this direction, the year, purposes, methods, research models, data collection tools, data analysis methods, research staff or populations and samples of the dissertations are presented as coded and in categories. The obtained data is presented in tables, and interpretations are done about the frequency and percentage values, and a general evaluation has been done about the dissertations about the differentiated instruction in Turkey.

Data analysis and finding

In this section, findings about the dissertation about differentiated instruction are presented respectively in tables in the direction of the purpose of the study, and interpretations are done according to frequency and percentage values. The first sub-goal of the study is “How are the dissertations about the differentiated instruction in Turkey distributed in terms of year and type?” The findings and interpretations related to this sub-goal are presented in Table 1. 

On analyzing Table 1, it is seen that most of the 19 dissertations about differentiated instruction conducted between 2001 to 2015 are doctoral dissertations. It is remarkable that most of the dissertations are doctoral dissertations. Considering the publication years of the dissertations, it is seen that there had been no publication about the subject between 2002 to 2008 and in 2009 and 2011. Even though there had been an increase in the number of the dissertations in 2013 and 2014, there was only one dissertation about the subject in 2015; and it cannot be said that there is an interest about the subject. That only 19 studies conducted about this subject within 14 years-2001 to 2015-shows that there is not a deep interest for the subject and it indicates the gap in this field. Considering the publication years, there were few dissertations related to the differentiated instruction earlier but there has been an increasing interest to the subject.

The second sub-goal of the study is “2. Which fields are the dissertations about the differentiated instruction in Turkey conducted on?” The findings and interpretations related to this sub-goal are presented in Table 2. On analyzing Table 2, it is seen that the 57.8% of the dissertations were conducted on science, mathematics and physical science. However, a very small ratio (5.2 %) of the dissertations were conducted on Turkish, social studies, preschool, classroom teaching and English. With this result, it is also seen that there has been no study conducted on visual arts, sport and music and there is a gap in these fields.  The third sub-goal of the study is “3. What are the themes of the dissertations about the differentiated instruction in Turkey?” The findings and interpretations related to this sub-goal are presented in Table 3.

On analyzing Table 3, it is seen that 34.6% of the purposes of the studies are about increasing the academic success of the students. It is seen that the studies are also about the creativeness (%18.3) and attitudes (%16.3) of the students towards the class. Moreover, the effect of differentiated instruction on the critical thinking skills, scientific process skills, learning approaches, academic  self-concept, self-efficacy perceptions, metacognition skills of the students is among the skills which are desired to be gained  by  the students. The views of the teachers related to the differentiated instruction are the subject of a few studies (8.1%). This study shows that the number of the studies related to the differentiated instruction is quite inadequate even though differentiated instruction has a positive effect on the academic success of the students. The fourth sub-goal of the study is “4. What are the research models of the dissertations about the differentiated instruction in Turkey?” The findings and interpretations related to this sub-goal are presented in Table 4.

On analyzing Table 4, it is seen that the researchers conducted their studies mostly on quantitative data (79 %). It is seen that control grouped and pre-test post-test quasi-experimental design was used in more than half of the studies (68.5 %). It is also seen that qualitative studies are at a very low percentage as 10.4% and mixed studies are also at a very low percentage as 10.4%. The fifth sub-goal of the study is “What are the data collection tools of the dissertations about the differentiated instruction in Turkey?” The findings and interpretations related to this sub-goal are presented in Table 5.

On analyzing Table 5, it is seen that most of the assessment instruments (82.6%) used in the dissertations are traditional assessment  instruments  which  can  be  found  in  every  levels  of education and are known by most of the teachers (Bahar et al., 2012). It is seen that among these assessment instruments, achievement test (30.7%) and creativeness test (15.3%) were used in the dissertations. It is also seen that scales which are used to evaluate cognitive, affective or behavioral performance were used in the dissertations. Among these scales, attitude scale (13.4 %) was used the most. Critical thinking scale, self-efficacy scale, cognitive skill scale and academic self-concept scale are also among the traditional assessment instruments used in the dissertations. It is also seen that questionnaires (9.6 %) which are used to determine the preferences in the face of a situation (Metin, 2014) were used in the dissertations. As it can be seen in the table, supplementary assessment tools through which both the output and the process are evaluated and which is more related to the real life than the traditional assessment tools (Bahar et al., 2012) were used at a lower percentage as 17.4%.The sixth sub-goal of the study is “Who are the research staff of the dissertations about the differentiated instruction in Turkey?” The findings and interpretations related to this sub-goal are presented in Table 6.

On analyzing the distribution of the dissertations according to their research staff, it is seen that the dissertations were mainly focused on the individual with superior intelligence. It is appealing that 57.8% of the dissertations focused on the individuals with superior intelligence as research staff. 31.5% of them were conducted on the individuals with normal intelligence and 5.2% of them were conducted on the teachers as research sample. In terms of schools, 63.1% of the dissertations were conducted on elementary school students. It is seen that primary school students were chosen at a ratio of 21% and high school students were chosen at a ratio of 10.5% as research staff. These results also show that the views of the teachers, parents and school managers were not considered about this subject in preschools. 

This study aims to analyze the dissertations about the differentiated instruction from various aspects. In the direction of this general purpose, the information about the publication years and themes, purposes, fields, research staff and data collection tools of the dissertations are presented in tables with frequency and percentage values. A broader perspective which would provide a general evaluation opportunity for the subject was created with the obtained data. Here under, the similarities and differences of the analyzed dissertations and general interest and drawbacks related to the subject was tried to be determined.

On analyzing the related literature, it can be seen that the number of the content analysis, descriptive analysis and meta-analysis studies about differentiated instruction is limited. There is only one study in which KaradaÄŸ (2014) analyzed the doctoral dissertations. In his study, KaradaÄŸ (2014) analyzed the doctoral dissertations which were about differentiated instruction and which were done in Turkey and other countries between 2010 to 2013.

Considering KaradaÄŸ (2014) study, it is seen that the dissertations in Turkey have some similarities and differences in terms of field of study, purpose, method and research staff when compared to those conducted abroad. It is seen that the dissertation conducted abroad focused more on the academic success of the students just like the one conducted in Turkey. On looking at the distribution of the dissertations done abroad by years, it can be seen that it is parallel with this study and there is not an increasing tendency towards the dissertations related to differentiated instruction abroad. These result show similarities with those of Karaduman (2010) about the importance and the necessity of differentiated instruction.

Another result which supports the study of KaradaÄŸ (2014) shows that the dissertations conducted abroad focus more on the academic success of the students just like the ones conducted in Turkey. However, it is revealed that not enough studies are conducted in Turkey including the perceptions, interests and attitudes of the school managers, teachers and parents about the differentiated instruction except its effect on academic success. This result is parallel with results of the study of Bailey & Williams-Black (2008) which investigates the views of the teachers about the subject. On analyzing the dissertations conducted abroad in terms of research model, it is appealing that the number of the qualitative studies conducted in Turkey is lower and the number of the qualitative studies conducted abroad is higher. It is seen that there is no difference in terms of research staff. Although the studies in Turkey were conducted more on the individuals with superior intelligence, it is seen that different groups like teachers, school managers and parents were also used in the studies conducted abroad. 

In the light of the related literature and findings obtained through this study, the results of the study can be summarized as follows:

The number of the  studies  about  differentiated instruction is inadequate and there is not an increasing tendency towards this subject in Turkey. Quantitative studies are generally conducted and these studies aim to increase the academic success of the students. It was found that different from the ones conducted abroad, the studies generally focus on the gifted individuals, and different samples are neglected. More studies are needed to be conducted. Studies which evaluate not only the results of the dissertations but also the results of all other studies about differentiated instruction.

The studies related to differentiated instruction are quite inadequate even though differentiated instruction has a considerable effect on the academic success, creativeness and attitudes of the students. Moreoever, considering the working fields, it is seen that physical sciences are mainly dealt with. Studies can be conducted on different fields like visual arts, music and physical education. Qualitative and mixed research models should be used in the dissertations and the studies about differentiated instruction.

Another result of the study shows that most of the conducted studies focused on the elementary school students. Considering these results, it can be said that different studies about differentiated instruction should be done in preschools, primary schools and high schools. In addition, it can be said that the studies should be conducted with pre-service teachers, teachers and school managers. 

The research staff should be diversified, the pre-service teachers, teachers, school managers and parents can also be chosen as research staff. It is thought that research models like ethnographic research, action research, phenomenological method, social theorizing, in which not only the result but also the process is included in the evaluation, should also be used in the studies.  

The author has not declared any conflict of interests.