I was really pleased to hear you have introduced the school to the delights of hedgehogs.
It isn’t normal, as such, for hedgehogs to still be around at this year, but there are often individual hedgehogs who are. I still have one hedgehog visiting here. I am not certain that she is a she, but I like to think she is (so I’ll probably turn out to be wrong!), but she was a fairly late hoglet and although she has spent a lot of time building a nest in a hog box (very conveniently right opposite the night camera) she is still around. Late hoglets may stay around, but they also may try to hibernate when they are too small and then will probably not survive. This year, in particular, the weather has been unusual in that we have been having a lot of mild spells, so it isn’t really surprising that some hogs have not yet hibernated. Possibly global warming? I don’t imagine there is much food ‘in the wild’ so it’s really good you are still feeding the hedgehog and water is important too.
My guess would be that the hedgehog there is a youngster. The only way to be sure that a hedgehog is big enough to survive hibernation is to weigh it. This may pose a problem if it is at the school and is visiting in the middle of the night. It isn’t really possible to tell by looking at them unless you have another one, of which you know the weight, to compare. If it is a cold night they often stick their spines up, presumably to keep slightly warmer, and so appear to be quite plump. They need to weigh at least 450g to survive hibernation. Having said that, hibernation is a dangerous time for hedgehogs and not all of them will survive, even if they are over that weight.
Regarding telling male from female, the following is a link which gives a good description and some photos of male and female youngsters. You may be lucky that a hedgehog decides to scratch in front of the camera so that you can see underneath. Alternatively, if there are multiple hedgehogs visiting, you can often work out who is which by their behaviour (although, I find this is easier if you are watching in ‘real time’ as opposed to being on video). During courtship the male will circle the female, often at length. She will turn round and round huffing. If you look very carefully, it is possible to identify individual hedgehogs from their natural markings. Keeping sketches of their markings is useful for this purpose.
Sorry this has got a bit rambly – there is so much to say about hedgehogs! I would recommend Pat Morris’s ‘Hedgehogs’ book, but make sure it is a recent edition. Just be aware that it was originally written a long time ago, so that there is some slightly outdated information – such as that about bread and milk, which it is now widely accepted is bad for hedgehogs. Also there is a good site with a lot of good information. Some of it is quite ‘academic’, but you might find it interesting.
There is, of course, also loads of information on Hedgehog Street.
Good luck with the hedgehog. I hope it has a safe winter and is joined by some others in the Spring.