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.
Student or Learner