A school in California told a boy to cover up his Star Wars t-shirt because it showed a fictional character holding a gun.

It may be a reasonable policy to exclude symbols of violence from the classroom, not because someone else was shot, but rather to avoid promoting militarism. It could also be a wise policy to prohibit shirts with commercial advertising, which this was.

Note that they did not punish the boy. US schools punish students for absurd reasons, even get them jailed, and that is a very harmful practice; but it did not happen in this case.