I finally sent my oldest (just turned 10) to school this year (4th grade). I wish I had done it when he was in 2nd grade but I was pregnant at the time and not thinking about that.
He had been very argumentative and uncooperative with me all along but it was getting worse last year in 3rd grade. Like many have mentioned already, there was the constant defiant and angry questioning (i.e. "Why do I have to do math!?"), malingering, disappearing, crying, learned helplessness, etc. It was taking about 7 hours, spread out, to do a day of teaching. I was worn out and the house was being disrupted in an unacceptable way. He had never been to a "regular" daily school and had no appreciation for the benefits of homeschooling in terms of flexibility, free time, curriculum choice, etc. Things came to a head because my second is 5 1/2, doing advanced K-1st grade work, and she was not able to get any attention from me with my oldest sucking up all my time and energy.
My DS initially was very fearful and scared of going to school (it's a small local private school) but he has thrived there, made friends and now likes it. All I need from them is to teach my DS structure because he is ahead academically and earning A's. He has four different teachers he sees everyday and he has to pack up his bag and go to their classes at a pre-determined time (same time every day) without arguing or malingering. He can't just throw himself on the floor and cry for twenty minutes if he doesn't think he can do a math problem (that he can do). He can't just disappear and expect his teachers to chase him down to do his schoolwork (like I had to do). He has to function like most kids (and people) and this has been good for him. He is up at 7:00 am, starts school at 8:00 am and goes until 3:00 pm. Then he has an hour of homework. On top of that he has four days of baseball during the fall and spring seasons and piano lessons and/or piano practice five days a week. The regimented schedule had him in tears the first month but now he sets his own timer for reading and gets started on homework on his own.
The rest of the house is much quieter with my DS at school all day and typically my worst day with my second is like my best day had been with him.
Ultimately, we decided my oldest needed the structure and the whole house couldn't be held hostage to his dysfunctional behavioral choices any longer. However, the plan is to bring him home either next year or the year after that. I really want to be in charge of his education at the middle level and beyond, and it can be difficult to have one child in a school setting (on that schedule) and the rest not. Besides it costs more than we want to spend and the public school is not a good alternative. So, I am hoping that this year (maybe one more year) will cement and inculcate the structure and work habits for good.
Hope that helps!