The Secondary School is made up of students from Grades 6 to 12.

Students in Grades 6 to 10 follow the IB Middle Years Programme (MYP), and students in Grades 11 and 12 follow the IB Diploma Programme, a preparatory course with university in mind that allows them to experience a holistic education with acute attention paid to academics as well as opportunities that suit the needs of students with a global outlook. Similar to the Primary School, the Secondary School has the support of an EAL and Learning Support Team, and two full-time counsellors who provide social and emotional support as well as career and university guidance. As a fully accredited school by the Middle States Association, our OSC High School Diploma is equivalent to a US-style diploma and is accepted by universities and colleges worldwide. Our students in Grades 9 to 12 collect credits towards successfully completing the OSC High School Diploma and most students complete the IB Diploma Programme as well. Our IB Diploma results have consistently been high and well above world averages.