To be honest, it isn't a big punishment. He desperately needs a quiet day doing little but potter around on the computer or colouring or reading because the term has been a long one. However he is not used to being grounded. He was concerned it would affect his computer privileges.
I let him off loss of computer time, but I stood firm. He was being cheeky and trying out the whole concept of 'teenage bolshy'. He is definitely challenging my authority and I consider that as I will one day be dealing with a fourteen year old possibly six inches taller than me and a good deal wider, I think I will exert my authority now.
I wish small boys came with a manual.
(he wasn't really that cheeky, he is still a sweetie)