Separation Anxiety in 6 year old

Curious to hear about any resources that you've appreciated when helping a kid adjust to school. My six year old is in first grade, first formal school experience and he’s not making consistent progress with his separation anxiety. It seems a big part of it is all the school breaks these days, he’s only had one full two week stretch this year so far and it was the best two weeks. Anyways I’m a bit at a loss of how to help him.