How do you give a boy a love note with out them knowing?

Answer 1

Get to school early and slip it in his locker. If no lockers were provided than placed it on his usual seating place in class. Perhaps you can find his home address and maybe mail him a secret letter and if that succeeds you might even be pen pals.

Answer 2

You could discretely slip the note into their bag or pocket when they're not looking. Another option is to anonymously leave the note in a place where they'll easily find it, like their desk or locker. Make sure your handwriting is not recognizable.