Andy Rotherham calls for parents to become more engaged in picking their child's teacher (and have the right to do so). Wow, this brings back memories of my parents carefully picking all of my teachers…

The most important decision you will make about your children's education is picking their school, right? That's the conventional wisdom, but it's actually wrong — or at best it's only half-correct. Teacher effectiveness varies a lot within schools, even within good schools, which means that just choosing the right school for your kid is not a proxy for choosing great teachers. So while "school choice" is hotly debated (next week is National School Choice Week, complete with Bill Cosby's blessing and events galore,) there are few rallies being held for giving parents the right to choose a particular teacher. That's because the whole system is stacked against empowering families in this way. In fact, because of how seniority rules generally work, it's a lot more common for teachers to choose their students than for students to choose their teachers.

Just how much individual teachers matter is the big implication of an analysis of 2.5 million students and their instructors that was released in December and highlighted recently in the New York Times.The long-term, large-scale study by economists at Columbia and Harvard used two decades of data to examine differences in student outcomes (including such categories as teen pregnancy and college enrollment) and link those differences with how effective their teachers were at improving student scores on achievement tests. The headline-grabbing finding was that replacing an ineffective teacher with one of average quality would boost a single classroom's lifetime earnings by a quarter-million dollars. And that's just from one year of assigning that group of kids to an average teacher instead of a lousy one. A second study, released January 12 by the Education Trust-West, an education advocacy group in California, examined three years of data on teachers from the Los Angeles public school system and noted that low-income and minority students are twice as likely to have teachers in the bottom 25% of effectiveness. The Ed Trust study did not get as much attention as the one by the Ivy League economists, but it reached the same obvious conclusion: more effective teachers boost learning for students.

The data are sufficiently compelling that these days it's only education's flat-earthers who continue to argue that teachers don't matter a great deal and that efforts to retain and reward the best ones andremove the worst ones aren't essential to improving schools. But for parents there is a more immediate issue: research shows that differences in teacher effectiveness are generally greater within schools than between schools. For instance, when analysts at the National Center for Analysis of Longitudinal Data in Education Research (CALDER) compared teacher quality at high- and low-poverty schools, they found relatively small differences between schools but substantial differences among teachers working in the same schools — especially in high-poverty schools where some really low-performing teachers created an extra drag on the averages. The researchers found that the best teachers in high-poverty schools were as good as the best teachers elsewhere. On the flip side, even "good" schools have lemons.

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