"The Case for $320,000 Kindergarten Teachers."

Great headline. Justified by the text?

The crucial problem the study had to solve was the old causation-correlation problem. Are children who do well on kindergarten tests destined to do better in life, based on who they are? Or are their teacher and classmates changing them?

The Tennessee experiment, known as Project Star, offered a chance to answer these questions because it randomly assigned students to a kindergarten class. As a result, the classes had fairly similar socioeconomic mixes of students and could be expected to perform similarly on the tests given at the end of kindergarten.

Yet they didn’t. Some classes did far better than others. The differences were too big to be explained by randomness. (Similarly, when the researchers looked at entering and exiting test scores in first, second and third grades, they found that some classes made much more progress than others.)

Where does the amount $320,000 come from? It's "the present value of the additional money that a full class of students can expect to earn over their careers." And that's not counting the social and psychological values that may flow from excellent early schooling. But salaries aren't calculated by the actual benefit the employee bestows on the clients. If it did, there would be some negative numbers. But what if kindergarten teachers were very highly paid? Different individuals would pick kindergarten teaching for a career....