there is no complete equality of students in a class in terms of development and achievement. Experience suggests that age, in particular, is not a valid measure of equality desired - perhaps - by the teacher. Social learning is based on the difference of experience. Material learning and knowledge acquisition are more sustainable when there is an 'educational gap' within the learning group, which is dominated by different pupils in different subjects.
The input from Hein Retter gives me clear recognition to my own student groups although I have not done systematical research regarding this question myself. This is an imortant question Khaled Mahmoud
Firstly thank you all for your answer. Maybe I should have explained more about my question, I am doing a research about developing multicultural awareness in non racial-diverse schools through educational games, and there are many researches done about ethnic diversity in classrooms and it's impact on students. However, I couldn't find researches about homo ethnic classrooms.