Thank you, that makes much more sense. And it also indicates there are more levels than just compacted math and grade-level. Now I get it!

To explain that diagram on page 7 (which was not clear to me until the incoming parent meeting for middle school):

The preferred pathway for kids not in compacted math in grades 4/5 is Math 6, then IM and Algebra 1.

The pathway for kids struggling in Math 6 is Math 6, 7, 8. Algebra 1 would not be until high school.

The pathway for kids in compacted math is IM, Algebra 1, Geometry.

Yes, it is. They have to offer the other courses for kids that are behind.

Pg. 7
http://www.montgomeryschoolsmd.org/uploadedfiles/curriculum/math/mathematics-program.pdf

I had believed this to be true, but now I'm confused because the middle school lists among its courses math 6, math 7, and Investigations in Mathematics, which implies 3 years of middle school math before algebra. Can a parent of a middle schooler explain it?