Summer Hours at the Robbers Library, by Sue Halpern

Fifteen-year-old Sunny steals a dictionary from a bookstore and is sentenced to a summer of community service at the local library.  Under the supervision of slightly misanthropic librarian, Kit,  and with the friendship of several library regulars, Sunny blossoms and Kit defrosts.  If you've seen the movie, "Running on Empty," you've got a pretty good notion of where Sunny has come from and is heading.