Class Size and Achievement, the Tennessee STAR Study

Because any analysis of students achievement that looks at existing differences in class size is going to have severe problems stemming from the fact that students and teachers are not randomly appearing in large and small classes, the gold standard of all class size studies is the Tennessee STAR study. This was a randomized intervention into Tennessee's schools that made for both small and large classes and randomly assigned students and teachers to both types of classes. The only non-random part was that school districts decided for themselves whether to participate.

Here is a summary of the program and the findings:

Star

Among those that question the results of this study, Eric Hanushek is the most notable. He remains unimpressed suggesting a number of deficiencies of the study but his major quibble is that all of his research suggests that teacher ability is hugely important and he thinks the 'random' assignment of teachers was probably anything but.