drew and tonya go to the same school because they are close to the same age and chris goes to a different school because his mom wants him to get a better education and the high school in the neighborhood is filled with violence.
Chris goes to a different school because in season 1 he was in junior high and Drew+Tonya were in elementary school.Also in season2 Drew was graduating into junior high while Chris was already in junior high .They went into a different school because Rochell,their mom,wants Chris to get a better education and go to Corleone Junior High while Drew went to SanfordLamont
the high school in chris's neighbourhood is filed with violence so his mother thinks if he goes to school with white children he will get a better education