We hugely promoted crawling for dd2. I've often mentioned my Attila the Hun techniques to teach crawling using the stairs etc... I have never met a physio (and we have had about ten or so, to date, that we have been very involved with) who has suggested anything negative at all about crawling. Of course, it's only part of the picture, and there should be a good schwack of appropriate weight bearing (using a standing frame as necessary) and physio stretches to make sure there is as little decrease in muscle/ tendon length as possible, but tbh contractures are part and parcel of spastic cp - hence the management strategies. Banning crawling sounds completely counter- productive in a ll sorts of ways.
Sorry, I know that was a while ago, but it's made me quite cross. How awful to be removing some independence from a child, and preventing development in that way!
There - we had a similar glitch around 3 - the physio took away dd2's walking frame, with the expectation that if we removed the support, she would begin to walk independently. It was the worst year, honestly. She was far less independent than before, we ended up using the major far more, and she was very obviously 'more' disabled, and required more support. After a year, they gave her a new improved walker (croc, my fave walker ever) and she was back to being miss independent again. After a further year she walked independently (and, as you know, she now skis/ whatever).
Sometimes it is just too soon to expect that level of development, but it doesn't mean that it won't be possible in the longer term - and I know it was just too early for dd2. She didn't have proper standing balance until nearly 5, although she could weight bear and hurl herself across the room, a la 12mo! So, don't give up, he does sound as though he is nearly there - just that he isn't quite ready yet.
I don't often get mardy with professionals (generally the whole thing thing is a 'suck it and see' experiment, and if it doesn't work, you move on to the next thing) but I'm ticked about the crawling.
On a brighter note, dd2 had ft 1-1 in nursery from 2yo - they gave her a free place from her first birthday due to her needs. She wasn't statemented until yr r. We did it in the final yr of nursery, so it was ready for school. Physio, OT and slt all went into nursery and liaised with the keyworkers and she had portage from early too. Tbh, I find there is a larger degree of acceptance for support with cp - in terms of provision, it's a much safer bet to have a cp dx than a social communication disorder - people have mostly fallen over themselves to help dd2, whereas ds1 was roundly ignored until he was 10...