It's all a question of the basic human material with which you have to work; at what level (English language, moral, cultural, educational, etc.) do you need to start?
I'll never forget the howls of protest from the specially selected, supposedly technically literate students of a prominent middle-eastern country on a sonar maintenance course at HMS Collingwood when an exam question included the use of Ohm's Law in the format I=V/R. They'd only been taught that V=IR.