Do you now of any research on the potential downsides of the opposite of this? I have a pre-teen son whose confidence with-- and enjoyment in-- maths outstrips his ability (although this might change in either direction). He's not cocky about it; he is more like "Damn. Only got a C. Oh well, next time..."

I can't see him hurting himself with maths, but if he decided he's gonna fix something electrical in a few years time, well that could be very bad indeed.