I didn't mean that you only get Ds if you are not well looked after.
I meant that this boy was a shoo-in for a A in that one subject (the rest were likely to be Cs) and he got a D in the one that was due to be an A (and Cs, as expected, for the rest).
The HT needs to ask for the review. Maybe s/he will even if no one outside the school points out what has happened to the boy. But if s/he needs a little prodding from the guardian, then, in practice, its not going to happen. Ditto if the boy needs help working out what to do next, then he's not going to get that from his (reluctant) guardian either. I think the boy's Dad was never on the scene and, in the back of my mind I think i remember that the mother stopped having anything to do with him when SS took him away when he was about 11.