Ebony & Ivory,
With very young kids (5-8 years old) I always do theory during their lesson time, because I know they will never do it at home. I have two good reasons:
1. If parents have never had any music education and try to help, they just confuse
children

, so they do most of their homework wrong (sometimes common sense is not quite enough for music)
2. If parents, however, had musical education (when they were kids and they hated it) and kind of remember something – they try to explain the way they see it. Again, I end up spending another lesson(s) to explain what I have already done. And my (bad) experience is that kids trust their parents more then me (which is reasonable), so I had to fight THAT, as well. I used to hear comments like:” But MY MOM told me to do this way!” and there was no way to convince the kid that his mom was wrong. After couple of similar cases I decided to stop giving little kids any homework, even if they only had to color the notes.
For older ones (10 – 17 years old) I use method which simply drives them crazy, so they have no choice but finish those assigned pages. This is what I do (and to be clear – I don’t do this on purpose!):
If they repeatedly come to lesson without having theory homework done, I keep explaining the same subject over and over again, with explanation that I have impression that they obviously didn’t understand what they had to do or how to do, since they didn’t do the homework. While I am doing that, I can see in their eyes that they don’t like it. I always make sure I put the date in their assignment book WHEN and WHAT we did, so after two or three lessons, when I have parents involved (first two lessons I give kids a chance to handle that on their own, but if pattern continues, I invite parents on the next lesson), both student and parent feel pretty embarrassed. Next lesson – they have everything done.
This always works, because the same kids usually don’t come to lesson without homework again, once they felt embarrassed in front of me and their parents. On the other hand, parents start controlling their kids more, because they also don’t want to be embarrassed again and they don’t want to pay me for doing the same lesson four times in a row, so THEY make sure kid is ready to move on. It just takes couple of lessons to do all of that slowly, but my experience is: it definitely works!
Good luck