I think most 4 year olds have trouble listening, and I'd be wary of a teacher labeling a child ADHD so young. Sometimes it's actually the teacher who is having the trouble because they don't have enough discipline and coping mechanisms in their own toolbox for every type of personality. My 4 year old ran rings around her first teacher, who labelled her troublesome, willful, undisciplined, the whole nine yards. We moved her to a teacher who had a different approach, and she's one of the brightest in the class, loves her teacher, loves learning and is well behaved during class play times. I think you're right to look at diet though. The main things I've tried to cut out are refined sugars and carbs, sodas (even non-caffinated) and anything with a large amount of artificial dyes, including those almost-glow-in-the-dark yoghurts! Try replacing them with fruit, water and 100% fruit juices, and whole grain breads and pastas. But, especially if your doctor is OK, then try not to worry too much, there are a lot of hyper kids out there, just being kids.