In high school, state and ETS (e.g. PSAT/SAT) tests were always required to be taken at a school from another district. For example, if you went to school in d

In high school, state and ETS (e.g. PSAT/SAT) tests were always required to be taken at a school from another district. For example, if you went to school in district A, everyone from district A took the test in a school building located in district B. The reverse was also true. This has always struck me as such an easy system to implement that I'm always surprised when I hear about the "teachers just changed the results" stories. While I'm sure this doesn't eliminate the risk of collusion, doesn't it dramatically reduce it? Plus, wasn't an entire chapter of Freakonomics dedicated to how teacher cheating can largely be caught algorithmically? In this day and age I would think it's even easier.