Since Miles became superintendent, Harrison's scores on state exams in math, reading, and writing have steadily increased. In reading, for example, 54 percent of Harrison students were proficient in 2005, compared to 61 percent in 2010. Critics who chalk those gains up to "drill and kill" teaching might find at least one thing to love about Harrison District 2: Its test score-based teacher-evaluation system is matched by intense professional-development efforts of the sort promoted by education experts from across the political spectrum.

But "really systemic, momentous things are happening right now, and I am at the ideological epicenter of that change," he added. "If nothing else, it's really interesting

Rival groups of education researchers interpret the reliability of value-added differently but even the technique's defenders have urged caution, as have the Educational Testing Service and the Department of Education's own Institute for Education Sciences. Experts raise a number of powerful objections: that value-added measurements are often based on poorly designed, unsophisticated standardized tests; that the ratings are particularly volatile (a teacher who scores very well or very poorly using value-added has only a one-third chance of getting a similar score the following year, and it takes about 10 years of data to reduce the value-added error rate to 12 percent for any individual teacher); and that the technique gives the impression that the teacher is the only factor in student achievement, ignoring parental involvement, after-school tutoring, and other "inputs" that research shows account for up to 80 percent of a student's achievement outcomes

A consensus is emerging on what those best practices are, and they have little to do with test-driven instruction. Research by Linda Darling-Hammond, a Stanford University teaching expert and former Obama adviser, has found that in Finland, South Korea, and other high-performing nations, teachers spend just 50 percent of their workday in the classroom with students, compared to about 80 percent for American teachers. During the rest of their day, Finnish and South Korean teachers work with other adults to plan lessons, observe one another's classrooms, and evaluate student work. This balance is especially important for beginning teachers; powerful evidence suggests that the single most helpful teacher-training exercise is to spend time inside a master teacher's classroom and to get feedback from that master teacher on one's own practice.

The teachers are grouped to maximize the sharing of best practices; one team includes a second-year teacher struggling with classroom management, a veteran teacher who is excellent at discipline but behind the curve on technology, and a third teacher who is an innovator on using technology in the classroom.

When I visited MSLA in November, the halls were bright and orderly, the students warm and polite, and the teachers enthusiastic -- in other words, MSLA has many of the characteristics of high-performing schools around the world. What sets MSLA apart is its commitment to teaching as a shared endeavor to raise student achievement -- not a competition. During the 2009-2010 school year, all of the school's teachers together pursued the National Board for Professional Teaching Standards' Take One! program, which focuses on using curriculum standards to improve teaching and evaluate student outcomes. This year, the staff-wide initiative is to include literacy skills-building in each and every lesson, whether the subject area is science, art, or social studies.

As Nazareno walked me through MSLA's hallways, introducing me to kids and teachers, she reflected on how her profession is changing. "I'm not afraid of being held accountable. I haven't dedicated a career to have kids unable to read or do science," she said. "But people need to understand that teaching and learning are very complex processes, and any time you try to measure anything that's highly complex, you can miss the nuances." Nazareno paused outside a classroom door and lowered her voice. "We had a girl in the second grade whose mother died. At the school next door, a girl was brutally murdered. That's all they've been talking about there for two weeks; they lost a lot of instruction time." She raised her eyebrows. "How do you factor that into value-added?"