Three things come to mind, listed with the most likely first:
1. He does very well in school.
2. He is very successful with the ladies.
3. He is a carpenter.
What does the expression "he's a school nailer" mean to you?
Maybe some wider context would help. That's something we usually request from posters, as single sentences might be ambiguous or meaningless.
PS: Welcome to the Forum
Last edited by charliedeut; 14-May-2013 at 13:04. Reason: Added PS
Please be aware that I'm neither a native English speaker nor a teacher.