Children with mental instability (ADD may be one form) almost always have more than one mental instability...
Anxiety drives most erratic or problematic behaviour, in Skinner fashion (Skinner was the guy with the dogs and the bells... the guy who pretty much discovered what is now called Conditioned Response) --child feels anxious, does something (washes hands, keeps a piece of trash, wriggles off the chair, counts, flaps fingers, pulls out eyelashes, bites nails) and feels less anxious. Behaviour 1, Anxiety 0. Repeat.
If the behaviour didn't do anything for the anxiety, it would quickly be extinguished... when it works sporadically --the first few times reliably, then from time to time, rarely, in a few bursts of successes -- it is reinforced to the point of addiction. It's how gambling, shopping, sex and everything else are addictable, too.
Allay the anxiety with healthier skills, all the erratic behaviour goes away.
at 8:11 PM on Mar. 27, 2011