You need a Grounds Gold Account to post on the NG BBS!If you don't have one, click here to sign up now! It's fast, free, and easy — and opens up tons of great NG features!
What are the chances that anyone who uses Newgrounds at your school will use that exact computer and actually come to Newgrounds during class.
Slim to none.
If you're that worried just change your password, and it'll invalidate the cookies because even though you were logged in, the password stored no longer matches your actual password.