Question

1. He doesn't see any students in front of the school.
2. He doesn't see any student in front of the school.
[Are both okay? Which one is common?]

Answer 1

Both are fine. #1 is probably used more often, but it would depend on what question was asked, to which this is the answer.

Answer 2

2. He doesn't see any student in front of the school.
3. He doesn't see a single student in front of the school.
[Does #2 mean #3?]