Having gone both to schools that don't measure their results using standardized measures, and those that do, with almost identical quality of teachers, the schools beholden to teach to tests end up being able to cover a lot less of substance. This is particularly the case when a school has been teaching to a test previously, and now averages about 95% per student on the tests; since their funding relies on improvements of scores, they've got to spend even more time preparing students in order to do better every year.