Russian School of Math

I have had two kids do RSM. One joined mid-year in elementary school and initially found it very stressful, but after that stuck with it for 4 years. After 8th grade they decided to do AOPS on their own over the summer, and just completed calculus at Laney as a freshman in high school (they felt too busy for RSM this year). My middle schooler wanted a break from RSM this year as well, but now wants to do it again next year because they realize how much more math instruction they got.
I wouldn’t say either loves math, but they do enjoy being good at it. They both felt like RSM challenged them and made them a lot better at solving problems than they would otherwise have been.

My kid is signed up for both, and enjoys RSM of math more, because it is easier. BMC is more conveniently located, and much cheaper. Their math problems are abstract. Their classes are large and mostly online at present, though some return to in person is envisioned for next year. Parental help is required, at least for the younger kids, because their homework problems are hard. Russian school of mathematics tests the kids and can place them at various levels, either online or in person. Their problems are much more concrete than BMC problems, though more abstract than what is taught at local schools. Classes are small. No parental involvement is required, because the homework is a straightforward application of the class lesson. BMC teaches students to think like a mathematician and invent techniques; RSM teaches specific math concepts using specific techniques. RSM is a business with many franchises; BMC is a public service run by sometimes-disorganized math professors.

Welcome to the Bay Area! I also started looking for math enrichment when my son was in first grade. The main options I found were Berkeley Math Circle, Firecracker Math, and the Russian School of Mathematics. We ended up going with RSM, due mainly to schedule and availability, but it has been fabulous. The closest location to you would be Dublin, but starting in 4th grade there is also an online class option. The best thing about it is that there are 3 levels per grade (accelerated, advanced, and honors), and all 3 are more advanced that what you will get in school. Most kids start in the accelerated level, but they will give a placement test and also make mid-year adjustments as needed. If the honors level is still not a challenge, they will move a kid to the next grade. They follow a curriculum, and introduce abstract thinking (variables) by second grade. You might also check out Beast Academy Online if getting out to Dublin sounds like too much or you want a less expensive option. There is plenty of challenge to be had in Beast Academy, and their programs for older kids, through Art of Problem Solving, are also really great. Good luck!

I want to strongly recommend the Russian School of Mathematics. My kids were also not challenged in school, and they weren't particularly motivated to do Khan Academy. They started, like most kids, in the lowest level RSM offers for their grade, and moved up the following year. RSM offers 3 levels per grade and does a placement test to make sure that each kid will be challenged but able to succeed. After starting RSM in 4th grade, my kids are doing algebra in 6th grade. RSM offers online classes if you don't live close to any of their Bay Area locations. Good luck!