Thoughts on middle-class children learning self-defence to avoid being mugged on bikes?

I have never had an issue of this sort.
I can't see any major objection to providing guidance of this sort to children.
My only concern with it (and, by extension, with an article on it) is that it may suggest that the risk of an incident of this sort is greater than it actually is with the result that even fewer children, middle class or otherwise, will use a bike to get to school. This is obviously a bad thing in public health, environmental and transport terms. If, for example, the data shows that while there has been an increase in incidents of this sort children are much more likely to (say) have their mobile phones stolen while at school such guidance would make less sense and may only serve to create the latest parental panic du jour.
And insurance companies will always be inclined to overstate risks to mitigate potential liability.
Proper data, explained in an appropriate context, is therefore everything.
In my experience very few children go to school by bike compared with the situation a few years ago and I don't believe that the number is increasing. It would be a shame to provide a further deterrent to doing so which is not supported by robust evidence.
Naturally, I appreciate that that perspective does not sell newspapers.