If you think the disruptive behaviors at pickup are attention seeking, you could try preemptively giving him attention when you first walk into the classroom, before you address the teacher. Also, I would not be surprised if he is bothered by the perception that you are talking about him in front of him, and he is not part of the conversation. Children have so little control over their lives on a day to day basis; listening to someone discuss your fate without your input just highlights that lack of agency. It might be worth investigating whether that is a factor. If it is, you could look for ways to give him some level of participation in the decision-making process, or at least a chance for his voice to be heard. And respected.

I have one who is extremely protective of this sense of agency, and has been since six months old. Also not particularly trusting of others. (Not distrusting either; just reserving judgment. ). We have to be discerning about talking to others about this child, when in earshot.

I forget which thread it's in, but the physical needs factor in behavior has been extensively discussed elsewhere, so it's certainly not a strange idea.

And one more thought: some of you may be familiar with the marshmallow test, as a measure of impulse control and maturity. Well, there's a variant of it, done in slightly older children, which found that successful impulse control had some correlation to the child's experience of their environment as being reliable and consistent. If the experimenter first kept a promise, children held out much longer on the marshmallow than if the experimenter first disappointed them in something else.

A consistent, reliable environment gives children a better basis for impulse control and delayed gratification.

...pronounced like the long vowel and first letter of the alphabet...