is not used in more United States schools. Even though there is a United States version of that series, most school districts that have considered adopting it have rejected it, as not having built-in scripted lessons for the teachers to present. I personally find it EXTREMELY easy and intuitive to teach lessons out of that series, to very good effect, but I'm not the kind of person who goes into elementary school teaching in a government-operated school in the United States. I do teach elementary-age pupils mathematics--that is my current occupation--but I teach them subjects that would be deemed "prealgebra" and "algebra" in terms of the United States curriculum.
What's your rationale for saying the other series is better?
After edit: yes, I am aware there are a few different textbook series under the title "Primary Mathematics" from Singapore publishers, but I haven't noted any significant differences among them. I still use the old third edition Primary Mathematics series adopted in Singapore rather than the new United States edition, for example.
It's been a while since I researched it, so don't remember fully.
One problem was figuring out which version of singapore math to get (for example the new one in singapore is not considered as good).
A bigger problem was that it doesn't meet state standards (I was researching for a school) and MCP does - while still being very good. (BTW they ended up using Addison Wesley grrr.)
Also an issue that some raised was the cultural differences that might show up. (Not a big issue, but why add obstacles?)
I think there was some issues raised that singapore math is not as flexible in dealing with students that have have varying learning styles, while MCP did a better job of that.
To a homeschooler this might not matter though.
But MCP really is very good and has none of those drawbacks. (I also looked at Saxon math, but it had WAY too much drill.)
Also, this is more of a "soft" reason, but a lot of reviews seemed to like it because it was from a different country. "They do well in school, so it must be the book." But I think cultural emphasis has a larger role than the book. There seems to be a lot of self-hate by homeschoolers - they don't like the schools, so they don't like anything american, therefor anything imported must be good.
I know none of this really gives a good answer for you. I had to pick something and MCP just seemed better.
Really, any people who like math, homeschooling or "afterschooling," could use it with their own families to good effect. Another favorite math series I learned about from homeschoolers, which I use with my own children in combination with the Singapore Primary Mathematics series, is Miquon Math.
Making Math Meaningful - not sure if it's still around - was what my mother used when I was homeschooled. It introduced concepts like variables from the very beginning, but without letters: one problem might be 1 + 1 = [ ]. A week later, you might see 1 + [ ] = 2. Eventually it just becomes intuitive what the missing box should be. Unfortunately, because I knew the theorums behind why you could do it intuitively instead of discretely, I had a hard time when I ended up in public school...
This is a pretty good page ("What Works Clearinghouse") for keeping up with "what works" in education. I'm linking this particular result here because of the "Singapore Math" connection, but their focus is on classroom use, not homeschool. They don't test things themselves, they just act as bullshit detectors.
http://www.singaporemath.com/Primary_Math_s/21.htm
is not used in more United States schools. Even though there is a United States version of that series, most school districts that have considered adopting it have rejected it, as not having built-in scripted lessons for the teachers to present. I personally find it EXTREMELY easy and intuitive to teach lessons out of that series, to very good effect, but I'm not the kind of person who goes into elementary school teaching in a government-operated school in the United States. I do teach elementary-age pupils mathematics--that is my current occupation--but I teach them subjects that would be deemed "prealgebra" and "algebra" in terms of the United States curriculum.