diamond back IMHE are very good value. Have a look at the new 2010 ( or 2009) Mr Lucky's ( DJ bike so no pegs) but discounted at various places and cracking spec and value.ie full cromo frame, forks, bars, decent rims 3 pc cranks,etc. Would be hard to beat these at the price (although iirc the tt is 20.75 inches so not super short).A cheapo jobby with a hi tensile frame could be had at a baragin prices for school duties though and is likely to have a shorter top tube too, if your son is small. Would be heavy but most are unless you start to spend. I would say a Mr Lucky is a Good BMX, although I have no experience of the more higher end ones,where you get a lighter bike, or additional strength for a given weight.