Hello Leslie,
Open Focus may be just the solution you need for your son.
There is no 'entrainment' per se (though it feels as if there is when I do it!), there are even programs for kids, and best of all for you: they claim ADD and ADHD are just ways of paying attention. Open Focus is all about learning to pay attention (narrow/hyper focus; soft focus; wide-view lens etc etc). You could do the sessions together with your son, and any other family members, so it might be more entertaining as you get to share feedback, results and real life applications.
There are two books, Open Focus and the other one Dissolving Pain with Open Focus. Both can be got cheaply via Amazon and come with a CD of Open Focus exercises.
I use it, though not for ADD or ADHD. So does NickR, also on the forum. Cannot vouch for the ADD/ADHD aspect, but if you read the Dissolving Pain book first, you will come across their claims. Here is the Open Focus site:
http://www.openfocus.com/products/You can see the Open Focus for kids on that page. However I would recommend you work with it, read the books (theory behind it) first so that you can help your son gain the best outcome for him. More nice news: you can use it with BrainEv - no worries about overdoing entrainment or anything!
Hope this helps,
Pure Bliss