[A]ny provider that commands 90 percent of the market—whether we’re talking about software, phone service, or heating oil—is, by definition, a monopoly. Our government employs thousands of bureaucrats to track down and break up monopolies on the grounds that monopolies stifle competition and thereby produce bad products at high prices. Doesn’t it strike anyone as strange that the same government protects its own monopoly in education? And stranger still, that nearly everyone accepts this state of affairs as normal—as something that has always been and must always be? ... [C]ompetition forces public schools into making long-overdue repairs. And it offers poor parents the choices they desperately desire.