My son's finishing 5th grade in mathematics and I'm also curious about the topic of what's supposed to be learned in standard 6th and 7th grade mathematics. When I look here

http://www.k12.com/courses/k-8-courses/downloadable-k-8-course-information/
http://www.k12.com/courses/scope-sequence/calms139 (6th grade)
http://www.k12.com/courses/scope-sequence/calms61 (7th grade)

there seems to be a lot of repetition of earler material (though maybe that could be said of all grades). Is 6th grade (what do you call it, pre-pre-algebra?) a grade that people routinely skip? Does that risk leaving gaps?

My son may have the option of skipping 6th grade mathematics, but I'm thinking it may be better to just go through 6th and 7th in one year (homeschooling), rather than skipping anything.

Any thoughts on that?