Complex sentence: Upon graduation from Boxwood PS, most of the grade 8 students will go to Markham District High School to study grade 9 because Boxwood is one of MDHS's feeder schools.
Split into simpler sentences: Upon graduation from Boxwood PS, most of the grade 8 students will normally go to Markham District High School to study grade 9. It is because Boxwood is one of MDHS's feeder schools.