We have looked at Caffeine as a treatment for ADHD before and the science indicated that it could have some benefits. As a footnote to this Wired has a report that regular small doses of caffeine are more effective than one single large dose.
Throughout the day, your noodle fills up with adenosine, a chemical thought to cause mental fatigue. Caffeine blocks the brain’s adenosine receptors, countering the chemical’s dulling effects. To maximize alertness and minimize jitters, keep those receptors covered with frequent small doses — like a mug of low-caf tea or half a cup of joe — rather than a onetime blast. Test subjects reported that periodic small shots made them feel clearheaded and calm, both of which enhance mental performance. Even better, add a lump of sugar or have a carbohydrate-rich snack at the same time for an extra cognitive kick. It seems that glucose and caffeine together do more to enhance cognition than either does alone.
Source: Caffeinate With Care: Small Shots Do a Brain Better Than Big Blasts. Note no reference to the research is given so please take this data with a large pinch of salt.