I homeschooled my daughter through end of second grade and we used Math U See for kinder, 1st, and 2nd. It's EXCELLENT. She is now in public school 3rd and the work they are giving her there in math is much more simple and sporadic and hard to follow. They're speed drilling her in simple addition when she was adding long columns of long numbers and carrying tens last year already with Math U See. I'll describe it to you a bit so you can see if it seems good for your son. Some homeschoolers I know prefer Singapore Math or another one...I forget the name of it...but I'm not familiar with Right Start.
Anyway, the beauty of MathUSee is that it thoroughly teaches every step of what the child is learning before moving to the next concept. You don't progress until the child gets it, so they DO GET IT. The manipulative blocks represent the numbers from units through tens and hundreds in earliest grades so not only do they learn their written numbers from 1 thru 9 and then tens and hundreds, they know what those quantities look like before they move on to adding, subtracting, multiplying them etc. So they don't jump right to memorizing "7+8=15", they actually know what 7 and 8 and 15 look and feel like, and different ways to build them.
Toward the end of second grade we weren't using the manipulatives much because she had moved on to understanding written numbers without them. You could absolutely use MathUSee at home in addition to school work (I am now), but school jumps around so much to different concepts, it would be hard to start from scratch and walk him through the last few years. But since he has learned in school, it may be much easier to go back and review basic foundation than teaching a child from scratch. You get lessons for each chapter in the year on DVD and in a tacher's manual which you watch and then teach, and then each workbook chapter lasts for about a week of doing a few pages per day.
You don't have to do ALL the pages if the child "gets it" but for the troublesome concepts sometimes we spent a couple weeks doing every page in the chapter...there is also a test book and fun math activities book for every chapter. So there still is a lot of written work and "worksheets" (book pages). It's not like some free-form building with blocks thing like some people think. It's very mastery oriented based in Classical style education.
I highly recommend, but some kids don't do well with manipulatives and go for one of the other styles. I find it was an excellent foundation for my daughter though and she's easily grasping what they throw at her in school even though her dad and I are HORRIBLE at math! I wash I had learned with MathUSee and then maybe I would not have been horrible.