Jinxed P:
It seems simple. ADHD is a problem with being able to concentrate. Meditation helps with concentration, and therefore would help with ADHD.
Perhaps not so simple. I think the name of the condition is a misnomer. ADHD/ADD is not necessarily a question of a
deficit in attention, but the management of attention.
ADD-inattentive types like myself can be quite capable of hyperfocus on subjects of interest. The executive function deficit, for someone who can hyperfocus, lies in shifting attention to other targets.
Concentration practices are easy for the hyperfocused, and concentration can serve as a "slingshot," if you will.