Possibly the most legendarily stupid boy I ever taught became a scaffolder. After he left school he seemed to dispense completely with consonants when he spoke. He told me he was an a-o-er. This could have been any number of things, but, model of patience that I am, I persisted and eventually through context managed to understand what was going on between his ears.
My pal Mel has a very amusing story involving this child*, logarithms and a mathematics inspector.
*If he survived his experience as an a-o-er then he will by now be in his 50s, I reckon.