We let our media specialist select the books. She often gets requests from the teachers too. Have you surveyed your teachers for their recommendations?
Otherwise, I'd make sure you have Caldecott Medal winners and Newbury winners.
If your school participates in AR (Accelarated Reader) then you'll want to purchase AR books and tests. We purchase new books/tests every year for the library, around $1500 each year. The first time we did this we sent home a survey home for parents and students asking what books they'd like to see. It was a long process but very imformative. The last few years we've left it up to the librarian to pick the books and tests and then we "approve" the list before we order. IMO, you'll want to fill in series that the library might not have all the books in, etc.
Best of luck
Our PTO wants to make every child an expert reader! We would like to stock our library with fun fiction books that will encourage kids (and parents of little ones) to read for fun. So, we are turning to the experts for advice.
What do YOUR kids bring home from school - and read?
What do you read to them before bed?
Our list will to be kept as an ongoing reference. We will purchase the books as we have money (and library shelf space) available. If you know of a company that likes to donate hard cover books, or a new turnstile, please let me know. I'd be happy to write them a letter!