You describe how our issues started, except we were at a gifted school in the pre school section.
If he is unhappy you need to listen to that! He may want to be using his time after school to just unwind, play, think, just be and now because he doesn't get what he SHOULD at school (where he spends a large portion of his day), he needs to do it at home in his free time.
Thats how my oldest son explained it to his therapist eventually. He had music classes, we did extra fun stuff, all of it stuff he enjoyed and loved. but he was unhappy and I still wish we had listened to the howling and screaming and quietness and lack of interest that followed and taken him seriously. It would have saved our entire family so much angst and worry and heartache...
I fail to see the need for him to complete class work before doing something interesting (although even his maths pack doesn't sound that intruiging for him). My son also would dawdle and not be interested in doing boring work. I can think of half a dozen smart kids who faced the same issue. Incidentally we are all homeschooling now - aside from 1 who is having major issues in their grade 1 class after less than a month of grade 1.
And I, too, would walk away from teacher and admin meetings feeling they were reasonable and I was odd/crazy/silly/weird/mad/pushy, whatever. But I wasn't and I wish I had trusted both him and myself more when I could have circumvented all the problems.
So I have no advice, except to say LISTEN to him. And take action. Either advocate for his real needs, or change schools or homeschool him.
best of luck!
