It's like in the reading by Ira Glass in which we learned that when classrooms were integrated the grade gaps between the lower black students and upper white students closed. When you have all of the low testing students together they will continue feeding off of each other and make little to no progress. The low level classrooms don't challenge the students with curriculum, so maximum effort isn't being put into schoolwork. However, when you keep the students unified, the grades will rise.
"Students who are placed in high-ability groups have access to far richer schooling experiences than other students"(Oakes).
Oakes discusses how the relationship between the teachers and students changes in different classrooms with different separations.
"In low-ability classes, for example, teachers seem to be less encouraging and more punitive, placing more emphasis on discipline and 'behavior and less on academic learning. Compared to teachers in high-ability classes, they seem to be more concerned about getting students to follow directions, be on time, and sit quietly"(Oakes).
This causes students to feel discouraged, which isn't what should be happening in schools. Integration for not only color, but everyone in general is key to successful students.