Regarding speech rights and potential offence, the very common way to prevent a problem is to have a school dress code banning any screen printed T shirts.
No graphics, no messages, no problem
Schools of every type in the UK have worn uniforms for years.
Retailers have responded to demand by offering durable, low-cost clothing that doesn’t necessarily need laundering after every wear.
As a result, there is almost no focus on clothing, status, etc.
There was a nascent uniform movement in some districts in the US but I imagine it was squelched under the indulgent Obama and leftist administrators.