In remarks at last week’s gathering, Mr. Gates said the foundation had seen success with some of the small high schools it helped create through its emphasis on that school improvement strategy, but that much of that work did not deliver the academic gains the foundation had hoped for.

“To be successful, a redesign requires changing the roles and responsibilities of adults, and changing the school’s culture,” Mr. Gates said. “You can’t dramatically increase college readiness by changing only the size and structure of a school.

So now the Foundation plans to focus more of its energies on "teacher effectiveness." That means trying to identify what makes for effective teaching, but it also means finding ways to "retain and compensate teachers based on their effectiveness, and help ensure that high-quality teachers are place in schools that need them the most."