Yes, school is a social environment for learning, that has value, but it's hardly the only way to obtain that. Outside of school, there are local clubs and hobbie groups, forums and blogs such as this on the Internet, alternate paths such as the military, etc. There are all kinds of ways to be around people who enjoy the same things you do, or are trying to learn the same things you are without going to school.
By saying thats a benefit of school you're implying that it's not obtainable elsewhere. School just isn't that important if you really want to learn, it's more valuable for those that lack motivation and need someone to make them learn.
In what country? Citation?
Here's some numbers from the UK: http://www.universitiesuk.ac.uk/faqs/showFaq.asp?l1=2&ID...
According to that, 43% of 17-30 year olds enter higher education in the UK.
For actual numbers of people in the UK with degrees, there's this page[4] from the National Statistics. For people of Working Age, 18 to 60-ish, in the UK, 16% have degrees, and another 8.5% have "Higher education qualifications". 15% have no qualifications. It would be handy to have data for the 25-35 age range, since not many 18 year olds have degrees.
[1] Type A: http://stats.oecd.org/glossary/detail.asp?ID=5440
[2] Type B: http://stats.oecd.org/glossary/detail.asp?ID=544
[3] World Stats: http://www.oecd.org/dataoecd/17/15/39245059.xls
[4] UK Degree Stats: http://www.statistics.gov.uk/STATBASE/Product.asp?vlnk=10446
My second point was not just that you can learn from your peers, but that there is a social environment at a school that is important, and not readily replicated in self-study. You don't learn much from your peers at a typical cooking class, but they still contribute to why many people choose to take classes rather than self-study.