Son Struggling to Focus

Hi Nicholeen, what we see in our 8 years old son is a struggle when it comes down to sitting still and doing his homework. Simple exercises that should not last more than 20 mins are turning into 45 mins, due to constant loud whining, kicking the chair, smacking the pencil, sometimes even tears. He gets easily distracted and can’t sit still. While he’s in this mode, I keep reminding him what a good job he’s already doing and that mistakes are normal. Not to get so frustrated, I ask him to keep his focus… then it turns into him being disrespectful to me. Raising his voice , saying that he knows! So I send him to a quiet space for 7 mins and go get him and ask him if he’s ready to take a deep breath and try it again 😖 suggestions? Ideas? I have added chores as consequences too. We already own your 4 books and read them every night.