These are libraries maintained by primary or secondary schools, private or public, for the use of students, staff and parents.
School libraries are often the first libraries that people are exposed to, and as such, have an influence on people's opinions of libraries in general, even after they are adults. I still remember my elementary school library quite clearly: the books, the brightly-shag-carpeted loft furnished with comfortable beanbag chairs, the high ceilings of the space. I sometimes remember it spontaneously when I smell school library books at a used book sale. Fond memories.
However, some schools are beginning what I see as a long-term trend: doing away with the books in their libraries and turning library spaces into communal media centers and "learning commons" where ebooks, computer searches and noisy collaboration and socializing take place, replacing the quiet, book-filled spaces that invite inner contemplation and losing oneself in the private dialogue between book and reader for long periods. This is undoubtedly the way of the future and perhaps public schools can't justify the cost and space of real libraries any more, but it is still a sad trend in my (hopelessly traditional) opinion -- and one that will likely lead to less reading (and certainly less deep reading), perhaps to less regard for books and even for knowledge altogether. We'll see.