We hear a lot about the need to put highly effective teachers in front of students year in and year out as the only solution for narrowing the achievement gap. In "Opportunity at the Top", Bryan and Emily Ayscue Hassel tell us how hard it will be to do just that. Running the numbers as they did for this exercise, we learn that no single strategy that's currently being touted will move us very far along.

For example, if we just got a whole lot better at recruiting smart, capable teachers, so that 40 percent of all incoming teachers proved outstanding--as opposed to their baseline of 25 percent--still only one third of all classes would end up being staffed by star teachers after five years of implementation. Similarly disappointing results would be achieved if we tripled the current dismissal rates for teachers (up to 6 percent from 2 percent). And again the same results for a strategy that would reduce by half the number of great teachers who leave teaching prematurely. All of these approaches still leave two-thirds of all classrooms staffed with less talented teachers after five years of implementation.

How can we improve the odds? To begin, the Hassels assert that it is necessary to attack on all fronts, using all of the identified strategies simultaneously. But even that multi-pronged strategy only increases the number of classrooms that could staffed by star teachers from 3 out of 10 to 4 out of 10.

Ultimately, the only viable set of solutions, they conclude, is to do all of the above AND expand the reach of these great teachers. Obviously, this means increasing class size. It also means exploring strategies that use real-time and asynchronous technology to teach, tutor or provide student feedback anywhere in the country. Only then can we expect in five years that the typical student experience would include a truly outstanding teacher in the classroom.