Too hard to solve?

The diagrammed position may be familiar with some readers, especially if you are a chess coach. It is the starting position for a common training exercise, where the players only have kings and pawns. I set it as part of a chess 'decathlon' for the ACT Junior Development Squad today (each round saw the addition of other pieces btw).
I had assumed that this positions would be reasonably easy to draw, assuming that there were no huge mistakes. However the more experienced players (as it was the first round of the tournament) managed to come away with a plus score, possibly due to tempting their opponents into making a poor move. There was only 1 draw (from 6 games), but there was also an upset win as well.
My instinct is that this position is drawn with best play, and feeding it into one of my chess computers seems to back this up. However this is based on a short search (24 ply or so), and there may be tricks hidden further down. Interestingly there has been some research in 'detecting blocked positions in the endgame', so I am assuming some work has been done that relates to this.