> They also help, by identifying bad teachers and bad schools.
Not really. Here in Chicago, the Noble charter high schools will often teach directly to the ACT. This results in some dramatic boosting of ACT scores, with some schools taking kids from the dysfunctional CPS System and getting a school average of 23. Unfortunately, once they reach college, they see little academic success despite being straight-A students with 25+ ACT scores.
This has a detrimental impact on the curriculum:
1) The English program structured heavily around basic reading comprehension, with little to no emphasis on writing composition. A students understanding of essay composition s roughly: "Organize the things you want to talk about into paragraphs... then write a conclusion." However, to their credit, they're really good at reading test questions.
2) Math is focused on teaching Pre-algebra fundamentals and then layering on test-specific Algebra, Geometric (with that goofy proof system), and basic Trig. It's a sad, narrow sample of our already sad & narrow HS math curriculum. It covers few "advanced" Algebra and Trig subjects. This means anyone who has to take "college math" will need courses in Trig and Precalc in college, with the possibility of an Algebra refresher course before proceeding.
3) Social Studies and Science? All rote-to-test. Students are drilled on step-by-step procedures on how to interpret graphs that'll score correctly on tests... without giving them actual knowledge on how to critically think about information - be it historical or scientific.
NCLB schools do the same song-and-dance, except with a much less rigorous test. If you've actually seen the questions on most NCLB tests, you'd be disappointed. Unfortunately, the composition of such tests is so political and messy it's impossible to provide any measure of quality.
You cannot assume testing will provide you accurate information or a better outcome for students. If you're going to implement a testing regiment, you need to be very mindful of the Observer Effect: You can very easily change the outcome by measuring it. This is not an easy problem to solve.