Hmmmm. Are you prepared to really give no presents?
After school, what is their routine?
Meaning...do they come home from school and do homework? Watch TV? Play games?
What if there's a no access rule. (which is what I do with Jon) Until ______________ (fill in the blank) is done...you get nada. Zilch. Zip. No video games. No TV. No phone. No friends. Jon has tested and lost. He gets mighty bored sitting in his room with nothing. And there was one time, where he flat our refused to do something (I forget what) and he was in his room for 2 days. (not straight...he went to school

) Nothing until rooms are clean. Nothing.
I see deals as a compromise. You give me something, I'll give you something.
AFAIC, chores are not a compromise. You do it or you pay.
Separate, but related, Jon has a very difficult time with organization due to his disabilities. I had so much trouble with him last year. He was in trouble constantly. So, I went and talked to his counselor this year. She said that I had to immediately reward and immediately punish him. So, if he brings home his planner signed, he gets $1. If he doesn't, he loses video games for the day. No questions asked. It has worked wonders. Now...I'm not suggesting that you pay them for doing what they're supposed to be doing. But, the premise has worked for us. Immediate reward, immediate consequence. Otherwise, the lesson doesn't stick for Jon.
Whoa...I rambled. Hope I've given you some help at least.