Can you take just night school classes if you are 16 and failed a grade

There is no one rule for every school in every country where this site is used.

1. where are you located
2. what type of night school
3. high school or GED program
4. why are you not merely going to repeat the class in regular school
5. is night class merely extra class to help make up classes while you also go to day school
6. and of course at 16 you can't do anything without your parents permission, so they will need to look into this for you