'4' obviously stands for '4th grade.'
Ah, the good old days. Everyone remembers those elementary school worksheets -- they were a pain to do at the time, but looking back as an adult, some of your own answers can look quite humorous.
But perhaps none are funnier than Oklahoma State quarterback J.W. Walsh's from fourth grade. The assignment was simple: Discuss how you feel about your decisions, and answer a set of questions about them. J.W. Walsh, naturally, related every single answer on the worksheet to playing quarterback.
For a good laugh, check out The Daily Oklahoman.