I feel like I am still new to this, but I can throw in my two cents...
My son did the same thing with his homework last night. It was simple, write his spelling words 3x & do his math paper. It usually takes hin 10-15 minutes max, but he sat in the chair for about 90 minutes working on it. He was distracted with doodling, playing with his eraser, talking to me, etc. I told him to finish up so he could go play, but he kept saying it was boring, he already knew how to spell these words, why did he have to do this, etc...
I decide I didn't care how long it took. I stayed calm & told him he could sit there till bedtime, but he was going to finish. He is a master at manipulation & continued to try & convince me why he didn't have to do it.
Long story short...from what I have read & learned on this website is that if it is not challenging, or exciting & new, than they have a hard time enjoying it & will avoid doing it.
I suspect your son may be bored with those things that take him a long time to do. That is the simple explanation that pops out at me. I am not sure the best way to deal with it, and I may be wrong, but thought I would share my limited knowledge of this topic!
