Both are used; both are fine. The problem is co-referencing. Plural uniforms could mean that each student has more than one uniform or that each student has just the one uniform.
1. Students are required to wear a uniform.
2. Students are required to wear uniforms. <can be ambiguous>
Context and/or paralinguistic information usually helps. For example, unlike 2. above, neither of these admits to ambiguity:
Let's get into our car. <one car>
Let's get into our cars. <two or more cars; one per person>
The second example doesn't have two meanings. The reason being, we know that in reality one person can't drive two cars at the same time.
All the best.
- For Teachers