> I believe that it was a better program than a median program, but I’m not sure if it’s because his peers came from families who could afford to spend time with their children, or if the program itself was better than median.

Doesn’t matter which is true. Early educational interventions fade out universally and we have nothing that effects adult intelligence or conscientiousness which explain pretty much all variation in educational attainment, partly through their effect on SES.

> “Heckman curve” update: The data don’t seem to support the claim that human capital investments are most effective when targeted at younger ages.

https://statmodeling.stat.columbia.edu/2019/04/06/heckman-cu...

> The Heckman Curve describes the rate of return to public investments in human capital for the disadvantaged as rapidly diminishing with age. Investments early in the life course are characterised as providing significantly higher rates of return compared to investments targeted at young people and adults. This paper uses the Washington State Institute for Public Policy dataset of program benefit cost ratios to assess if there is a Heckman Curve relationship between program rates of return and recipient age. The data does not support the claim that social policy programs targeted early in the life course have the largest returns, or that the benefits of adult programs are less than the cost of intervention.