I don't think reading the POH is very common among PPL students. It was never even mentioned to me, nor to anyone else I know.
Yes, well, since the trip (thread "How to be Dim" IIRC) where I couldn't work out how to make the radio's display bright enough to be readable I have always made sure I've re-read the POH within living memory before flying anything on my own, and will now do so for ever. As we keep saying, we must learn from each other's mistakes - I lived to learn from mine, not everybody does.