It feels like we've become a broken record arguing against class size reduction initiatives as a cost-effective investment for increasing student achievement (see here, here and here.) The main reason there's no bang for the buck in these initiatives is that they rarely make much more than a dent in lowering class sizes. But here's a fresh report with a new twist: teacher effects can be just as influential on student achievement as major reductions in class size.

Data that were originally used for Project STAR—the famous 25-year-old Tennessee study that showed truly small class sizes do have a positive impact on student achievement—was put to use yet again, but this time to study teacher effects on student achievement in grades K-3 using a random study design. The key finding: if a student has a highly effective teacher three years in a row (kindergarten through second grade), his/her growth in reading by third grade would equate to the same amount of growth as being placed in small-sized classes in the early grades. Math achievement would show positive effects as well, but not as much as in reading.

Of course the rub here is that in this case, "highly effective" is defined as a teacher at or above the 85th percentile of effectiveness. Not a lot of those to go around.

Clearly, finding enough "cream of the crop" teachers to have these kinds of effects on student achievement is no easy feat. But the payout is great. We're talking the equivalent of a third of a year's reading growth in third grade that can be attributed to the lasting effects from a student's kindergarten, first and second grade teachers. This growth exists in addition to the achievement effects of the child's third grade teacher.

And just to be clear, the cost of reduced class sizes as measured in Florida over eight years was $18.7 billion, a pretty penny if highly effective teachers can produce the same results.