I'm listening with great interest. My 10 year old 4th grader is currently doing NEM. We homeschool, so clearly it is self paced and isolated. But I'm not sure the alternatives. I know my 10 year old might be able to do AoPS online classes, but I just think the work load would be too much for him at this point. I'd love to find him a math team or something more "social". But feeling stuck where we're at.
Locally a college has a talented math program for 6th to 8th graders to get them through college math in I think amounts to 2 or 3 years. It's rigorous with a heavy workload. But the social piece would be good. I might bide our time doing NEM1/2 until he could test into that. You are supposed to be highly prepped for college level math at that point if you do well in it.
I'm actually really impressed with NEM as a curriculum. It is not quite a deep as AoPS, but really very close in terms of conceptual understanding and leaps. We went to NEM because we went through Singapore 6B and you can't really jump from 6B into AoPS without a bridge. But now I'm liking NEM. I have a math degree so I really overthink our math curriculum options!
