Heck yah!
My kids are allowed one treat a day - that includes cookies, chocolate, whatever, and it is always after noon and before 6.
You can see the direct effect - they jump around, get hyper, and sometimes even shake their heads like crazy people.
One of the things they tell parents of kids that may have or are diagnosed w/ ADD or ADHD to do is to change their kids diet.
It's not just sugar, artificial colorings can cause hyperactivity and some kids are particularly sensitive. For some reason, it is common for Vets to warn dog owners (particularly of small dogs) to avoid giving them human food w/ food coloring because of this, yet we let our kids have this stuff all the time!
i think sometimes we feel like those processed foods give us a break, but we forget how simple it is to make a pb&j and don't need to buy the pre made ones! it's worth the effort!
But aside from their diet, it could also be the acting out is to get the attention of the busy parents...then the busy parents quiet them down (or end the harassment) w/ treats...etc etc...
Also, aside from the food - a lot of kids get soda, and soda w/ caffeine which compounds the problem...