A suggestion has been raised in comments here by way of a response to the questions that ex-home educating lawyer Ian Dowty posed here.
The suggestion, which only exists in vague form at present, is that there be some sort of compulsory, perhaps annual lecture, delivered by local authorities or another designated body to home educating children and their families on the subject of children's rights, abuse and how to solve the problem of abuse. It would not involve assessment of children and families but merely ensure that children know about how the government conceives of children's rights.
Several commentators mention some problems with the idea of a summer school for example, but I wonder what they would think of the more limited proposal above?
I have to admit I am tempted, as I have this vision that the whole thing would rapidly proceed to a demonstration of how it is actually HE children who are routinely listened to and have their rights respected and that it is schooled children who are woefully abused by the system; (see Cosmic Seed's tale of woe in the comments below).
UPDATE: In response to some criticisms of the idea, one proposal is that the method of delivery of information be much more flexible than I delineated above. For example, a child could be given a book at a health centre that would be appropriate for their age and ability, a health visitor could help them read it and that a lecture would therefore not be the only compulsory option.
FURTHER UPDATE: From comments, we have a suggestion that discussion/information/training on children's rights and how to stay safe be offered by the state on an invitational basis, with the idea that it is more likely than a compulsory scheme (which abusive people would make an effort to dodge) to reach the people who might need help.