Standardized tests mostly show whether you are good at taking standardized tests.
Having coached students in leading “test prep” programs, having done well on the tests myself, and having watched students and my own children take numerous standardized tests, I can absolutely confirm: they are not great predictors of subject mastery. They are excellent predictors of which students will do well on future standardized tests.
We are talking at the moment about rich people spending money to cheat on their kids’ tests, and that’s fine, but I really wish we could step back and talk about the fact that the test itself isn’t good. They’re just no good for measuring human beings and predicting their future success.
Oh, I almost forgot. Standardized tests are really good at predicting the per capita income for a school district.