The evaluation of 12th class exams typically depends on the educational board or system in your region. Generally, the exams are evaluated based on a combination of internal assessments and external board exams. Internal assessments may include periodic tests, projects, assignments, practical exams, and class participation, while the external board exams are conducted by the respective educational boards. The specific weightage given to internal and external assessments may vary. The final grades or marks are usually calculated based on the overall performance in both internal and external assessments.