Criteria for evaluating school choice mechanisms are first, whether truth-telling is sometimes punished and second, how efficient the match is. With common knowledge preferences, Deferred Acceptance (DA) dominates the Boston mechanism by the first criterion and is ambiguously ranked by the second. Our laboratory experiments confirm this. A new ex ante perspective, where preferences are private information, introduces new efficiency costs borne by strategy-proof mechanisms, like DA. In a symmetric environment, truth-telling can be an equilibrium under Boston, and Boston can first-order stochastically dominate DA in terms of efficiency, both in theory and in the laboratory.