I was a habitual runaway as a teenager, starting at 15. The first time I ran away I was held hostage for 5 days by a man who repeatedly tried to rape me, and assaulted me in various different ways. A class would have been nowhere near as graphic as the experience I had, yet I was only home for about a week before I ran away again. My shortest time out on the street was a day, the longest was about 7 months. There were no missing posters, no searches, nothing. Sometimes I would think about how if anything happened to me, who would know? Who would know who I was or who to tell about what had happened to me? There were lots of times where I was hungry or cold or sick or scared. Yet, every time I got sent back to foster care I would only last a month or two before I was gone again. I really can't say why I did it, there were a lot of reasons and there were few good ones. I decided that I was tired of it and I wasn't going to do it again, I'd seen some scary things happen and I was tired of going to jail. I lasted two months, then my foster parents son molested me and I ran again. This time I was 17 and a half and just managed to age out of the system. I got pregnant a couple weeks after I turned 18 by a guy who was 25, and I married him even though he beat me because I was tired of running and just wanted a home and family.
I guess, long story short, I don't know that a class outlining the risks to runaways would do much good. Most kids that run away habitually already know the risks, and the one-timers generally get too spooked to try it again, or they get the thing they wanted from their parents, etc. There isn't a good explaination for a lot of it, other than kids have a general sense of immortality and refuse to accept that risky behavior can have horrible consequences.