Mercersburg uses a trimester system with fall, winter and spring terms. Students can take year-long (3-credit) courses or trimester (1-credit) courses to fulfill their requirements.

Each student must carry a minimum annual course load of 15 credits of academic work at each grade level or the equivalent of five year-long courses. These annual course requirements must be met from offerings in English, fine arts, history, language, mathematics, religion, and science. Students must also meet the indicated physical education requirements for each grade level.

All students board and study on campus during the last full year prior to graduation; they must pass all spring term work in order to graduate.

The diploma requirements for a student are determined by entry grade.

Junior entry: requirements for students entering in the ninth grade
Lower-middler entry: requirements for students entering in the tenth grade
Upper-middler entry: requirements for student entering in th eleventh grade
Senior entry: requirements for students entering in the twelfth grade