Tammy, I've been down this road. School send us down this road... the wrong road.
It is so easy, when kids "can" exercise control
some of the time, to assume that when they do not, it is because they
choose not to.
We found that if the carrot was big enough, difficult child would pull out all the stops to make X happen - but then something else would go wrong, because he didn't have enough resources left over to sustain the behavior. Yes, it's easier when they "always" or "never" do something. But the "sometimes" cases are not necessarily a matter of the difficult child choosing to behave that way.
Example: When things started getting really bad at school, WE noticed (school refused to believe us) that he was better in the morning than afternoon, better on Monday than on Friday, and so on. THEY (school) said he just "didn't want to" cooperate. Fast forward a few years to answers and... a severe Auditory Processing Disorders (APD) meant that difficult child was spending ALL his mental energy just trying to hear the teacher, and by lunch time he was totally beyond coping. A good night's sleep brought him part way back, but not all... so the next day he burns out faster. Technological intervention for Auditory Processing Disorders (APD) = WAY less effort to listen = WAY, way less behavior problems.
But because he could listen "some" of the time, the assumption was that when he didn't, it was because he "chose" not to.
And that's only one of a long list of issues and challenges that all had the same sort of pattern. He can... some of the time, under "perfect" conditions... and the rest of the time, he actually can't.
If you want the whole list... let me know and I'll send by PM.