My daughter is only in kindergarden, but she does get homework. It might only be writing letters & numbers and coloring pictures that start with the letter they are studing. Well, and they are to read the supplied nightly books for at least 30 min a night & over the weekend. Anyways - I help her read the directions on her worksheets, then she tries doing it on her own, but if she ask for help - I help her, I look over it & I have her correct whatever she did wrong after explaining to her what was wrong and why, then we read her books & do her word flash cards (they want the kids to know 100 sight word before the end of 1st grade & her teacher as sent 1 word home a week for them to work on to help them know them early). Eventhough she is in kindergarden - we spend about 45 min doing homework a night, except Friday... I take Friday off - lol.
My older daughter (now a freshman) lives with my in-laws... they use to go over her homework & I believe they still do some, having her correct what was wrong. The only complaint I had about them was that if they felt she had to much homework, my mother-in-law would do some of it using her left hand to write so it looked like my daughter did it. Now that my daughter has to do it all on her own, she doesn't have the study skills she needs to do the whole homework load & chooses not to do it. Which does effect her grades.
As for your son, if you feel he is able to learn the way you teach him - keep helping him. If the teacher wants to see which once he got wrong... maybe you could rewrite the problems you find incorrect on a piece of notebook paper & have him redo them there leaving the incorrect answer on the origainal paper. That way the teacher can see that he got some incorrect, but did redo them and get them correct. It might help her to see issues your son might be having & help to give the class more lessons in those areas instead of leaving kids behind not understanding what they are doing. Thus, helping you and your so feel he will be able to pass the TASK test.
Also, you mentioned that he has dyslexia & other issues... has your son been tested inorder to place him correctly. You stated that he would do better in a smaller class size... sometimes you are able to get this if he is tested & they find this to be helpful for him. I have dyslexia & I was given a tutor to help me in my weak areas... I'm not a stupid person, I just needed someone to help me find my way of learning - which wasn't like everyone else. Once I found my way, my grades were alway very good and even in college my grades earned me honors... as I got older the only way people knew about my dyslexia was if I told them or they cought me on a day I was super tired & had a harder time "fighting" it.
Don't give up on your son! Although that is what you are being asked to do... the teacher is wrong here. Just try to find a way of helping him & keeping everyone happy. Good Luck!!