My just turned 3-year old son has zero and I mean ZERO attention span for any structured activity but can focus for hours on items / activities of hist interest. Part of our problem is that he has no interest in "age appropriate" things and activities so he'll run, cry, scream, kick or go into a silent blank face shut down mode. He does have High functioning autism diagnosis but from what we're seeing at home, the attention span thing seems to be unrelated to his diagnosis. He is right now into trying to force ME into HIS structured activities! lol