What I've seen working in middle school is that I think students have not been introduced to algebraic concepts EARLY enough! They're afraid of "x" by the time they get to 8th grade. Algebra looks like a foreign language and they don't realize they've been doing "what plus 5 makes 10?" for many years already.

My own DS is 7 1/2 and I'm teaching a pre-algebra pull out at his school. They're all excited to be free of adding two digit numbers.