We bought this for my son when he started middle school.  This backpack is super lightweight, has pockets in all the right places and is extremely durable (believe me, my son can really bang up his stuff).  Paying a little extra is worth it for a great quality backpack. The wheels are smooth and roll without any problem. Zippers are strong and don't catch.

Update: My son still has this backpack and is holding up as much as any poor backpack put into my son's possession is possible. He still loves it and uses it daily.