GAW: It seems I was wrong and there is or was a small Jewish class in a Monsey public school but it’s being contested because supposedly the goal is to have kids mainstreamed. Even eating Kosher meals separately is considered smacking of segregation by some… I found the above in a Tablet Mag article titled “The Blame Game” which is very informative on this topic.
I couldn’t find the article I thought I remembered which also mentioned Williamsburg. I may have read it offline and I’m not sure by whom. Sorry.
I don’t know the details of the Willamsburg program, but it’s not a religious class per se so it’s during regular school hours. It’s most likely deemed cultural, hence the accommodations are possible.