The Value of School; Actual Data

This morning I see two kinds of data on the aforementioned "human capital" (vs signalling and ability bias and whatever else there may be) theories of the value of school. First, an international study, examining the failure of schooling to boost national income in various low-income countries. Why Is the National Return to Education So Low?

For human capital extremists, schooling increases income - national and private - by teaching useful skills. So if low-quality schooling fails to boost national income, it should also fail to boost private income.
This prediction is the opposite of the truth. In low-income countries, the private return to education is unusually high.

And obviously that tends to count against the idea that schooling, the specific extra schooling in the specific countries being examined, increases income by teaching useful skills such as "how to think" or whatever. Instead, we have reinforcement for signalling and/or ability bias.

Another kind of data comes from a proposal that I've heard many times over the years: year-round schooling. After all, we don't need the kids out in the fields with the crops any more, so they can learn an extra 30% more or thereabouts in the same number of years. Indeed, if you spend the summer forgetting part of what you knew, your schooling is less effective in teaching useful skills -- so 30% ought to be an underestimate. Is it? Does (constant #days) year-round schooling matter?

This paper presents a human capital model to illustrate the conditions under which these calendars might affect achievement. We then exploit the natural experiment to evaluate the impact of year-round schooling on student achievement using a multi-level fixed effects model. Results suggest that year-round schooling has essentially no impact on academic achievement of the average student.

Again, that counts against the human capital theory and in favor of ability bias and/or signalling. Sigh.
Or then again, maybe I'm missing something.