Measuring teachers by how much value they add to their students' tests scores is an idea that I advocated back in the last millennium, and has since become the state of the art conventional wisdom, and, now, it is being implemented into universal law in Colorado, all without anybody actually showing it does a whole lot of good. Dana Goldstein has a funny article in the American Prospect, "The Test Generation," about what that actually means in the classroom:

On exam day in Sabina Trombetta's Colorado Springs first-grade art class, the 6-year-olds were shown a slide of Picasso's "Weeping Woman," a 1937 cubist portrait of the artist's lover, Dora Maar, with tears streaming down her face. It is painted in vibrant — almost neon — greens, bluish purples, and yellows. ...

The test asked the first-graders to look at "Weeping Woman" and "write three colors Picasso used to show feeling or emotion." (Acceptable answers: blue, green, purple, and yellow.) Another question asked, "In each box below, draw three different shapes that Picasso used to show feeling or emotion." (Acceptable drawings: triangles, ovals, and rectangles.) A separate section of the exam asked students to write a full paragraph about a Matisse painting.

Trombetta, 38, a 10-year teaching veteran and winner of distinguished teaching awards from both her school district, Harrison District 2, and Pikes Peak County, would have rather been handing out glue sticks and finger paints. The kids would have preferred that, too. But the test wasn't really about them. It was about their teacher.

Trombetta and her students, 87 percent of whom come from poor families, are part of one of the most aggressive education-reform experiments in the country: a soon-to-be state-mandated attempt to evaluate all teachers — even those in art, music, and physical education — according to how much they "grow" student achievement. In order to assess Trombetta, the district will require her Chamberlin Elementary School first-graders to sit for seven pencil-and-paper tests in art this school year. To prepare them for those exams, Trombetta lectures her students on art elements such as color, line, and shape — bullet points on Colorado's new fine-art curriculum standards.

Studies prove that Yale graduates with high-paying jobs tend to have stronger opinions on the merits of Picasso v. Matisse than do high school dropouts in prison, so, logically, that proves that we can't start lecturing children too young on Matisse and Picasso, because if they don't go to Yale, they're bound to go to jail.

Anyway, the question I have about measuring public school teachers through value-added testing is this: How many private schools do that? We have thousands of private schools in America, but I can't recall ever hearing of one that regularly uses these now fashionable value-added assessments to measure teachers. Why not?