Parents seem to like it, so something can be said for face validity. My experience has been unfavorable. It seems to me, and research seems to support this, that children referred for ADHD all fail the test. The reason I gave the TOVA was to determine children's behavior when under stress. The task is so boring.
Kids tend to start moving around or they fall asleep.
It gives my good information about how they deal with the stress of the non-reinforcement or the boredom of a task. But to use it as a diagnostic tool, I wouldn't.