I bet you are the 'only parents who make their son stop playing with' an X-Box, Game Boy, Lego, football - whatever just happens to be the trend at the moment ,because nobody else has to do this!'
You are exactly as totally unreasonable as parents always were, still are and hopefully evermore will be, for their kids education needs. Of course it didn't used to start until a bit later - but I can easily remember having such unreasonable parents when I was at school myself, even though I'm 68 now. I could be 'a right little madam' when I wanted to be though funnily enough 99% of reasonably well educated adults admit to the same.
High BG does indeed make us grumpier than usual - but adolescents of either gender are most definitely grumpy anyway. You could try striking a dad/son deal with him. Explain that you've researched it and discovered that high BG always makes T1s grumpier than normal - but since you aren't him so never know whether it's that or not, can he simply reserve his grumpiness for when he is high. If he agrees, then say good - and then test his blood every single time he grumps! - no exceptions 'just in case'.