I think addition and multiplication can be learned together easily- they are pretty similar, if you think about it. This can be done in first and second grade. Subtraction is harder, and division (although you wouldn't think so), is harder too. Maybe third grade, maybe fourth. Lots of repetition helps.
I agree with you! I think the USA in general doesn't do a good job pushing math forward for kids. They water it down and ask little, at least where we are. (And our public school is in the top 5% of California for STAR math testing too!).
I explained to my third grader over several days how to divide 2 digit numbers into 5 digit numbers. It took several tries but he got it! It's a fifth grade math book. He's gifted but honestly, I think you could get other kids to understand that too before fifth grade with a little elbow grease.
