Hello student that may vary from school to school and the reason why you want to repeat class 11 again, if you got failed in class 11 and you want to repeat it again yes they allow you to do the same as you're a bona-fide student of that particular school.

I request you to please help me with the reason why you want to do that so I can provide you exact information.

Feel Feel to comment if you have any doubt

Good luck