we had this with DS1. i think it's often a maturity thing (it definitely was for him)
he was horrendous for tears, tantrums, pleading on his knees he couldn't do it, all through yr 7, and most of yr 8.
he just couldn't be bothered really, because most of the time when he actually got over himself, he could do it in minutes.
we were always consistent, and he always had to do it (even if it wasn't always his best work - which he then got called out on by teachers at parents evening, with us there).
now he's in yr9, and in the last 4 months he's really turned a corner. i think it's dawned on him that he'll properly be on the GCSE treadmill in a few months, and he needs to stop fucking about.
in the same timeframe, he's become much more mature and aware outside schoolwork (eg, his responsibility to his football team, what he needs to do to maintain meaningful friendships, and his attitude to the wider family).
lots of other boys in his year are still like he was in yr 7 in terms of attitude.
it might just be a timing thing.