Database normalization for School Management System
You don't model GRADE_SECTIONS at all.
Unless your school has a massive programmr of demolition and construction every summer holiday the classrooms will be the same. It is the assignments which change each year. So CLASSROOMS should be assigned to a separate GRADE_SECTION entity, instead of merging SECTIONS and CLASSROOMS as you do now.
Students should be assigned to GRADE_SECTIONS not CLASSROOMS.
COURSES should have many EXAMS rather than many EXAM_RESULTS. It simply doesn't make sense that a French Exam could be taken by students learning Maths and Russian.
The line from Attendance (many) should be drawn to the Classroom_Student (1) instead. Drawing the attendance to the students is not possible I think.