Volunteering in a school library would show you very little of the skills needed to, for instance, conserve valuable rare books, assist seekers of obscure information and arcane knowledge and/or thrilling tales, (okay yes you probably did some of those last few for the kids) supervise book lending between branches and to individuals across a city or county, get volumes digitized, maintain the ability to lend tools, kitchen and craft equipment, and various non-paper media, preserve local history, negotiate with political boards and potential donors, manage teams of professional and volunteer employees, and keep the fascist book-burners at bay.