It turns out that teaching language arts, math and science to fourth graders is not the same as manufacturing cars on an assembly line. That is, the microeconomics principle of economies of scale—or the cost advantages that businesses get by increasing the scale of production—do not always apply to educational interventions. Put another way, an intervention that works great in one specific educational setting cannot necessarily be “scaled up” to work in many other settings. This is the finding of a major new study funded by the National Science Foundation, on which Associate Professor of Psychology Steven Stemler collaborated with…