This weekend I was at a party, and a bunch of parents were talking about their kids' experiences with math. The kids they were talking about were all fifth- or sixth-grade girls. Every one of those parents talked about how their kids had been in tears with frustration over their math homework. I've heard similar stories from other parents as well.
This seems crazy to me. What do we think is so all-important about fifth-graders knowing long division (or reducing fractions, etc.) that it's worth regularly making them so frustrated with the subject that they're reduced to tears? It doesn't seem crazy to wonder whether we're asking them to do stuff that they're just not ready for -- or at least that would be much easier a few years later.
Chris, I also had a fifth-grade girl in tears over her math homework. It's terrible. It sets the child up to hate school, hate math, and doubt her own abilities. It's one of the many experiences that has made me a campaigner against homework in elementary school.
But I can't agree with your second paragraph. You ask, "what do we think is so all-important about fifth graders knowing long division?"
You should know that Everyday Math, and other constructivist math curricula, don't teach long division. They teach "partial sums division", an extremely long-winded and error-prone substitute. Since they don't teach the standard multiplication algorithm either, the amount of work they propose to solve a simple division problem is mind-boggling. Here's a video showing their methods:
Why is a child struggling with math? It could be that the child is simply too young for the concepts being taught. Or it could be that the child is using a lousy math curriculum that doesn't really prepare her for each next step in learning math, and presents a collection of time-consuming and inefficient strategies instead of teaching standard algorithms.
If your child is using Everyday Math, I assure you that the curriculum is itself a huge source of frustration. Is she also too young for the concepts being taught? Actually, I doubt it. If you tried teaching her fractions and long division yourself, you'd probably find she was perfectly capable of learning them.
All of us who send our kids to traditional schools run into the issues you describe. The problem is that it isn't really up to us to make decisions about what gets taught when. Your fifth-grader will soon be going to middle school, and soon enough she'll take Algebra. When she gets there, if she can't handle fractions, she will be in deep trouble.