heres a link to a very usefull and unique bag : http://www.myawesomebuddy.com/2011-10-04-13-25-04/features
The 'A frame'
The ‘A-Frame’ back system gives the child a custom fit, all the time. Buddy’s ‘A-Frame’ back system is designed such that adjustments can be made to custom fit in 3 simple steps. This means that the ergonomic school bag grows with your child, ensuring a perfect fit all the time. This also means big savings as you wouldn't need to replace the ergonomic school bag just because they got bigger!