Children from wealthy and impoverished families attend the same school, but everyone wears the same uniform. This promotes social tolerance. Children don't bully those who are less well-dressed. As a result, they grow up slightly less aggressive.

Unlikely. Seriously, I often see such arguments, but I've never seen children compare clothes in my life. Phones, as Ples suggested, maybe. Clothes? Really? On the contrary, the more tattered your jeans, the more authoritative you are; this is obvious.
So, they are more likely to grow up narrow-minded and insecure because they cannot dress in what they want. Or (in the case of brainwashing, as with Artsa), they become ultra-patriots who, by definition, behave aggressively towards everyone who does not belong to their social group.