I think it's worth doing a string test to get a rough idea, but I have doubts about the accuracy. On my own two youngsters, it has my 2 year old Finn (currently 16.1-2 hh) maturing at 18.2 hh and my yearling Fiona (currently 15.1 hh) maturing at 19.1 hh.
On both horses, their dam is 15.2-3hh and the sire is 18.2 hh.
I admit I don't know all that much about horse genetics, but I do know dog genetics, and puppies of two different size parents tend to finish somewhere in between the range of the two parental heights, not under, and not over.
In my case, I would not suspect either Finn or Fiona to get much over 17 hands matured, despite what the string test says.
Last edited by Indyhorse; 06-13-2011 at 03:11 PM.