The damages of consistent advertising:
"Supersize Me" section were first graders are interviewed (Biased source)
This isn't even placed into a school-like scenario, but just advertisment from the home. Notice how they all recognized the logo character of McDonald's. This takes the edge off of smaller businesses (even downsized Wendy's in this scenario) as they aren't as easily noticed. That means the big businesses like McDonald's, due to it's immense advertising budgets, can easily steal money from other struggling businesses who need the customers to survive, thus chipping away the "American Dream".
There was also a heavy incident with Credit Cards being advertised in College environments. Several Credit Card companies, for a price paid to the school mind you, were permitted a certain day to advertise, promote, and sign students up for their merchandise. Some just had their stand ready to welcome new signers. Others had small gimmicks like free pens or T-Shirts with a signature. Either way, several of the students went for it. Many of these students found themselves swallowed whole in credit card debt due to lack of money management skills. Of those, there are cases of suicide in which the student realized that he/she was in a pit that they can't climb out of. Although this situation can easily be blamed on their poor budgeting skills, advertising is clearly a direct culprit of their deaths. (Oh, and by the way, the companies then began to charge the dead ones' parents for the bill.)
Now onto what it can potentially do when pushed in the Elementary/Middle/High School Educational Sector.
You have to remember, no matter what THERE WILL BE ADVERTISING IN SCHOOLS. It doesn't have to be a McDonald's banner in the football field, or Coke being sold in Vending Machines. Advertising is shown on peoples clothes, the backpacks people wear, the water bottles people drink from, and even the textbooks they use. (Houghton-Mifflin seems to have a near monopoly on these.)
The "Pros" of advertisement:
1. The added budget to the schools for more beneficial funding like a new gym or newer editions of Houghton-Mifflin textbooks.
2. Brings in more interest to the school making them more likely to excel academically.
3. Sometimes supplies students with equipment or clothes from their favorite brands.
4. Adds more options for the schools.
The "Cons":
1. Easily recognizable brands take business away from the smaller companies.
2. Establishes what is "Hot" and "Not" on school grounds, causing segregation of some students who do not have the latest material.
3. Brainwashes kids into a "He who has the most toys wins" situation.
The Flipside:
1. Sometimes the advertisements are from less popular companies bringing more attention and business to them
2. The children will be advertised to at home anyway, so it may not really cause all that much damage
Personal experience:
1.The advertisements everywhere on the football field and Basketball Gymnasium were really annoying.
2. An earthquake drill was announced and followed by "Sponsored by Pepsi". It didn't make me want to buy Pepsi, and was odd to hear an advertisement for that sort of event.
My Opinion:
Advertising does damage, but is a necessary evil
Either way, even if the schools took advertising completely out, students themselves would still be spreading advertising through clothes and whatnot. And if they made uniforms a requirement, they are still advocating advertisement, but for a singular company.