Talking with reference to Class 12th Marks,there's no such criteria in GRE/GMAT exams.All you'll need is a valid GRE/GMAT score that'll help you get a better college/University in foreign.But if you'll talk of GATE,since it's an Engineering Aptitude test,it's score is valid in every Indian Institutes & a selected lists of foreign universities also considers admission based on your GATE score, which include National University of Singapore (NUS) and Nanyang Technological University (NTU) in Singapore and Technical University of Munich and RWTH Aachen in Germany.