It depends on what?
The comma in the poll statement is unnecessary.
Sorry to correct you but otherwise you won't learn :-P
It is perfectly correct; there's no need for a comma if the if- clause comes after the condition.
It's better to say, "If you don't correct student's mitakes...". "Correct a student" sounds like putting a student into a correctional institute.
Also, we cannont use "they" here because they talk about one student, not many.
You can use "they" instead of "he or she" when referring to a singular correlate.
good students will do it on their own bad ones need to be corrected
it depends of the way that you use for doing it.
They can be used as a gender neutral singular pronoun