I can't link you to the Chinese or Japanese materials, because I bought them in Shanghai and Tokyo. Also, they aren't written in English. The Googlers next door use Russian materials from Moscow, also not written in English.
It's hard to do better than Singaporean materials, which are in English and modified (not in a bad way) for the US market, which you can find at SingaporeMath.com. Their Primary Mathematics series is superb. I use the Standards Edition, which is said to track the California State Math Standards. That sounds ominous, but actually the state standards are excellent. The districts essentially ignore them by using a ridiculous "reform" curriculum that, being "a mile wide and an inch deep," will always include a checkmark every year for any topic you can think of, thereby covering anything mentioned in the state standards (superficially and in random order).
Note that for these Asian curricula, you REALLY need to know how to teach the math. The textbooks only provide visual aids and example problems, not the tutorial text (paragraphs of explanation) typical in US books. If you go for Singapore Math, you should get the Home Instructors Guide (at least for a few levels), which teaches you how to teach it.
And DON'T start a kid at too high a level. Use the placement tests downloadable from singaporemath.com to decide where to start. It's all about carefully building up from the bottom, mastering each level before moving on.
It's hard to do better than Singaporean materials, which are in English and modified (not in a bad way) for the US market, which you can find at SingaporeMath.com. Their Primary Mathematics series is superb. I use the Standards Edition, which is said to track the California State Math Standards. That sounds ominous, but actually the state standards are excellent. The districts essentially ignore them by using a ridiculous "reform" curriculum that, being "a mile wide and an inch deep," will always include a checkmark every year for any topic you can think of, thereby covering anything mentioned in the state standards (superficially and in random order).
Note that for these Asian curricula, you REALLY need to know how to teach the math. The textbooks only provide visual aids and example problems, not the tutorial text (paragraphs of explanation) typical in US books. If you go for Singapore Math, you should get the Home Instructors Guide (at least for a few levels), which teaches you how to teach it.
And DON'T start a kid at too high a level. Use the placement tests downloadable from singaporemath.com to decide where to start. It's all about carefully building up from the bottom, mastering each level before moving on.