I looked into clubs a few years ago. Unfortunately, the only thing I was able to find were ski clubs that occasionally included a bit of wakeboarding.
A water skier needs a slalom course, which is a fair expense, a lot of work to set up and requires regular maintenance. Since a slalom skier can't really practice his sport without the course there is a real need for clubs.
Wakeboarding is different. You don't need a course. Paying dues to a club doesn't really buy you anything.
An amature slalom competition is pretty easy: Either you made the buoy or you didn't. Wakeboarding needs judges, ones who know the tricks and can tell the difference between a backroll and a scarecrow. Reasonable judges can be hard to come by in a typical club organization.
If your neighbor is just interested in some amature competitions there are a few around. The water ski club at Don Pedro and the club at Modesto work together to have some fun competitions. My son competed a couple of times. I wouldn't recommend joining the club but it can be fun to give a low key competition a try.
Note that the competitions were based on skill level, NOT age! If your neighbor's son can land an invert he will be in the advanced group, competing with adults. On the other hand, if he his best trick is a wake to wake jump with perhaps a grab then he will be in the beginner class, competing against the little girl who wins because she smiles so nicely......
If your neighbors intentions are just to get their son into an environment where he can learn faster then the best bet is to grow a circle of friends. Do your neighbors have a boat? Can they ride during the week?
There is nothing like peer pressure to push your limits. Having another rider in the boat that is as good or perhaps a little better can really accelerate the learning. Such riders are actually easy to come by, just look in the "find a third" section of this forum.
Wakeboard instruction can help a lot. There are two good places within a short distance of you: Discovery Bay Ski/Wakeboard center and Yoshis Norcal Wakeboard camp (925-584-4488) at Orwood marina. I highly recommend Yoshis. The instructor is Josh Smith, was a pro and has been teaching for a number of years.