WW notes, "Standards are currently mandated in many states."

In Maryland, not only are standards mandated, but the legislature (the biggest collection of useless pinheads on the face of the planet) has also, imitating other states, mandated tests at various levels (3rd grade, 8th grade, 11th grade, I believe) to check on the schools' performance in teaching the mandated content. This has resulted in the phenomenon of "teaching to the test". In order to have students score as high as possible, teachers, with the support (nay, the direction) of principals, spend their time teaching only what will be covered by the tests, so as to have maximum time to cram the kids for the test. Anything not expected to be on the test is rigorously excluded, as taking up valuable time for no good end.