Like the first season's Sacrifice, we are presented in this episode with a sort of "alterna-Charlie." What Charlie might have been if he had tried to impress someone other than his big brother.
However, this was not done to show Charlie growing, but rather show the growth Charlie has already accomplished. Megan brings Charlie along because he will be helpful in talking to the boy and because Charlie would understand (but not necessarily over-sympathize with) his plight.
The bad-guy with a stutter was a little much. A little silly, really. But the inclusion of Bill Nye the Science Guy nulls any negatives in that regard. Seriously, it is funny to think that he was probably one of the few people ever in the history of Numb3rs stars and guest stars who actually understood his dialog without an explanation. Too bad there was no bow-tie.