So I have been doing this prank too many times, thought I would share it with you. In my country you can buy school chalk candy which looks exactly like school chalk, if you can get it in your country it would be awesome. Now replace it with the original school chalk & also if your class has a store replace that too. In this way you are sure to waste a lot of the boring school & it's also pretty funny seeing your retarted teacher trying to write with it :O