I must have missed all the "good" stuff. All I got from this thread was people dribbling on about flying a 172 in VFR conditions with positive air temps up past 6,000 feet.
A new student is taught that that possible icing can happen in up to 5 degrees positive, Its pretty wise to be conservative when you have NO experience in icing, It sure beats the new instrument student that gets his ticket and blast of into a cloud without any regard to ice like that one story in AOPA's "Never Again" here recently
but a new student should also be taught the difference between "can happen" and "is happening". When in conditions it "can happen", be extra vigilant, aware and have a plan. If it turns into "is happening" then execute that plan, whether it be climb, descend, etc.
On a 172 you have that little OAT guage you fixate on, but just on the other side of the window there is the the probe for that guage, and that is where ice is going to form before it starts on the wings. So if the OAT says its cold, stop looking at the guage and pay attention to the probe part of it outside the window and watch for the ice.
The tires. The tires (since they are black) are the first place you will see icing if you're in it. That's what I include in my scan in fixed gear birds. BTW, sometimes things will stick to the tires that aren't sticking to the wings, so its a bit more sensitive.
You learn by doing. Just don't try to learn until you're ready to do. In your pants. But seriously. This is an example of things working as they should, he did it, he diverted, he learned something. There's nothing to see here, put down the pitchforks. Better this than winding up a statistic, or flying in VFR conditions in FL for 1000 hours and then deciding he's ready to be a 777 pilot, or (worst of all, maybe) going all the way and deciding he's invincible. Would he have made it? I dunno, I know *I* would have. But that's not the point. This is the education of an aviator, and he's doing it like he should, one step at a time. You done good, kid.