Very few games can be played when you're at school/work because most of them ask for undivided attention. If you had internet connection, you could always leech on DTV server. Obvious singleplayer choice would be any turn based game, such as old Civ, HoMM3, stuff like that where you can pause for unlimited amount of time and go back to the game like nothing happened.
If you want to play FPS, SUPERHOT or its newest variant
SUPERQOT is the best choice imo.