Schools have been getting healthier and healthier over the years. I remember being a little kid and getting adequate portions. In my high school years, have the meal was vegetables and fruit, and the meat and potatoes were half the size they used to be. I would always be so thankful to get home, so I could eat all of the good food I was missing all day. Chips, Quesadillas, ice cream, cheez-itz, whatever was filling. (not veggies) Oh I had such a need for food by the end of the day, hours before my family meal. I'd eat chips till the salsa ran out. If kids want to eat the good stuff in controlled portions during school, I say let them. They teach how to eat and exercise but they don't trust you to do it anymore.
Students who buy ice cream in school, not only gives more money to the school, but also can be something that makes school more enjoyable for the student. Eating ice cream before or after a test could potentially help calm the students nerves. While it may not be a healthy choice, nothing is stopping them from having it outside of school.
No it may give them hyper and it will make them want to stay up all night and they will not have good grades when they are sleepy in school they will also forget what his or hers homework was and a lot of kids would like to jump around when they have sugar.