Screen time limits aren't working because 'homework'

So my 12yo now has to use a Chromebook for basically everything at school. Then he says he needs the iPad for research. Then it's messaging his group project friends. Then it's 'just one game.' By the time evening hits, he's crushed his screen time limit and I don't even know if I was right to enforce it since some of it technically was school. How are other parents handling the blurred lines between school tech and recreational tech?