General Instructional Programs 13A.03.02.06
D. Student Service. Students shall complete one of the following: ....
(1) seventy-five hours of student service that includes preparation, action, and reflection components and that, at the discretion of the local school system, may begin during the middle grades;
(2) a locally-designed program in student service that has been approved by the State Superintendent of Schools.
Service Learning background: Maryland's graduation requirement
From the MSDE website, here's the requirement: