Horatio,
Ultralights is correct to an extent. It's called situation awareness you smart arse.
You don't just fly up to the edge of a thunderstorm of low cloud bank and go "oh bugger, I need to divert now".
I'm not advocating telling students where a diversion will be during an upcoming flight, however, diversion training doesn't really teach much decision making anyway. How often does an instructor just say "ok, now take me to X"? A better technique could be explaining a simulated weather event ahead and get them to make a decision. If the decision is not really suitable some further prompting could be given.