I would think the water would be way too cold for swimming just yet. It's only been in the 40s at night and hasn't been consistently warm enough to maintain a warmer water temperature. So, unless the pool is indoors or heated, I would think it would be too cold.
Would you be going too? If so, you can check the water out yourself and see what you think. And, if you let your son in the pool, just watch his reactions. If he starts to shiver or gets goosebumps, tell him it's time to get out. That's what I would do anyway. I don't see any reason he shouldn't go to spend time with his classmates even if he isn't in the water a whole lot. They may all decide on their own that it's too cold and play around the pool deck.
Hope this helps.
God bless,
A.