Agreed. I could have (and sometimes did) passed every high school exam with decent grades (~B+) without studying, just by having actually learned the K9 material during the previous years. However, what I got out of the experience was 2 things:
First, I got a better grasp of the breath of human knowledge. It was mostly shallow, mind you, but in my mind it was like a buffet. You sample a little bit here and there, and figure out what you like and what makes you good (or sick).
Second, it is the social interaction thing. I think this is important, but not in the way you imply. What I learned most in high-school in this aspect was:
* How to deal with assholes.
* * What to do when you are forced to be around with assholes.
* * There are many kinds of assholes, and you should not deal with them in the same way (i.e. You can escalate conflict and make the typical bully back off, but this might prove a horrible mistake if attempted on the truly violent psycos).
* * Assholes can climb into positions of authority too (aka asshole teachers). You need to know how to fly under their radar.
* Dealing with Authority.
* * Authorities are not necessarily competent or event interested in fulfilling their nominal roles. You have to educate yourself.
* * Authorities do not care about your problems. You have to figure out and solve them yourself.
* * Authorities are very interesting in maintaining the status quo. You do not go around shaking the waters without reason.
* * * Unless you figure out how to turn status quo disruption into leverage. Then you go for it and turn authorities into unwilling allies in your dealings with assholes.