Andrew Clements 
Janitor’s Boy [EPUB ebook] 

Ordinarily, no one would have imagined that Jack Rankin would vandalize a desk. But this was not an ordinary school year for Jack….When Jack Rankin learns that he is going to spend the fifth grade in the old high school — the building where his father works as a janitor — he dreads the start of school. Jack manages to get through the first month without the kids catching on. Then comes the disastrous day when one of his classmates loses his lunch all over the floor. John the janitor is called in to clean up, and he does the unthinkable — he turns to Jack with a big smile and says, "Hi, son." Jack performs an act of revenge and gets himself into a sticky situation. His punishment is to assist the janitor after school for three weeks. The work is tedious, not to mention humiliating. But there is one perk, janitors have access to keys, keys to secret places….