But what about those who cannot keep up as efficiently as others? Do you leave some behind or do you teach to the lowest denominator? Should those who are not able to perform to the standards of the class abandon math altogether?

I think that instead of breaking different mathematical categories into different years, one standard math class should be taught year to year. As in as the class reaches the middle of one group of associated patterns of math another is introduced to supplement the material of the previous, and on and again. In depth overview of topic, what the topic actually means, and then how it relates to the topics before and after it. You could introduce geometry and then incorporate reasons why it ties in to trigonometry.

All in all I suppose I would say that teaching about the subject before teaching how to use a subject would be my view. Just build two steps forward, one back, one to the left and then one to the right, and keep building until you have a solid foundation instead of just laying down blocks without taking the time to cement them together.

I know this is pretty similar to what you just said.