Hi there, I know a third year B-tech CSE student at NIIT University (NU). I am not sure about other engineering colleges which provide admissions based on your 12th grade marks, but NU gives a lot of weightage to consistent academic performance in school (Marks in 10th and 12th grade marks) in its admission process.

To get admission into NU, make sure you have secured more than 60% marks in your 10th and 12th grades. NU gives a lot of weightage to your academic performance in X & XII and also have an innovative selection process of ensuring that they find the right students.
In addition to X & XII marks, NU gives weightage to its own admission interaction process  where the focus is on interacting with the student rather than through a single entrance exam. Also the scholarship is offered based on X, XII and Admission Interaction Process. There is a scholarship check after 2nd year of your undergraduate program, so you have to maintain the required CGPA, for example, as of now I am enjoying 100% scholarship in my tuition fees as my 10th score was 94.2% and I had 93.2% in my 12th grade. I now have to maintain 7.5 CGPA score after my 2nd year of B-Tech program, provided which I will continue to enjoy the same scholarship.
Hope you got the answer you are looking for. Thank-you