Incidentally, I also recommend the sequels to Hatchet, Brian’s Winter and The River. Neither are as good as the original, but both are good in their own rights.
There was also a sequel to Island of the Blue Dolphins that I think I read, called Zia , but I don’t remember if it was any good or not (I read a lot of books as a kid, it seems)
Another couple of books that come to mind for me are The Cay by Theodore Taylor, and The Sign of the Beaver by Elizabeth George Speare, both of which I read in the 6th grade.
Oh, and speaking of the 6th grade (a time in my life when I didn’t read books, but rather consumed them as quickly as I could get my hands on them) there is also Caddie Woodlawn by Carol Ryrie Brink.