My two children, a boy and a girl, are both 10 years old (fraternal twins) and just finished 4th grade. They're homeschooled so we don't exactly follow the New York State curriculum (shhh, don't tell the district superintendent) and only use a formal curriculum for mathematics (Saxon).
Since we like to have a general idea of how they're doing, we do give them standardized tests at the end of the year (but we don't "teach to the test" in any way) and they recently had the California Achievement Test (CAT) from Seton Testing - a nationally normed standardized test.
My daughter had an overal composite percentile score of 97 and my son's was 96. The only section not in the 90's for my son was Language Mechanics at 80th percentile and the only section not in the 90's for my daughter was Comprehension at 67th percentile (personally, I think she rushed through it or something because she does nothing but read at home and I'm sure her comprehension is better than that).
And here's the difference between public schooled kids and homeschooled kids. In public school, my kids would just move on to the 5th grade. In homeschooling, my wife and I look at these scores and say Emily, you have to work more on comprehension and Lucas, you have to work more on grammar. The education is tailor made to both the kid's strengths (what do you want to study?) and weaknesses (what do we need to work on?). No one gets left behind and no one advances until we know they truly understand the material.
It's not for everyone but so far has been working well for us.