Not an ideal answer but a better answer

A longstanding question with an answer. How much does education improve intelligence? A meta-analysis by Stuart Ritchie and Elliot Tucker-Drob. From the Abstract:

Intelligence test scores and educational duration are positively correlated. This correlation can be interpreted in two ways: students with greater propensity for intelligence go on to complete more education, or a longer education increases intelligence. We meta-analysed three categories of quasi-experimental studies of educational effects on intelligence: those estimating education-intelligence associations after controlling for earlier intelligence, those using compulsory schooling policy changes as instrumental variables, and those using regression-discontinuity designs on school-entry age cutoffs. Across 142 effect sizes from 42 datasets involving over 600,000 participants, we found consistent evidence for beneficial effects of education on cognitive abilities, of approximately 1 to 5 IQ points for an additional year of education. Moderator analyses indicated that the effects persisted across the lifespan, and were present on all broad categories of cognitive ability studied. Education appears to be the most consistent, robust, and durable method yet to be identified for raising intelligence.

I long ago took it for granted that the obvious answer was that yes, more years of education would yield higher IQ. As I took more statistics and more biology, I reversed that opinion. Over many years I have seen innumerable reports of highly varying quality and approach arguing one way or the other. I settled on the view that it was possible that there might be some effect but it was likely small and that there was a residual issue of persistence. Would interventions to increase schooling lead to an artificial increase in score which might then revert to an underlying mean over time?

This is the first study I have seen in a long while which seems to move the dial a little bit. It is a meta-analysis which poses its own problems but overall the researchers seem to have been knowledgeable and diligent in attempting to address the criticisms attendant to earlier research. The identify a whole range of excellent additional questions that remain to answered.

The fact that there range is so wide, one to five IQ points, is disappointing. One point is effectively, given the topic complexity, within the margin of error. Five points could be real and a five point increase in personal or societal average IQ could have significant positive consequences. It would be nice to know where in the range is most probable. The fact that they find a consistent persistence in IQ (i.e. the effect is not temporary) is interesting and positive.

I don't think these results are large enough or rigorous enough on their own to substantively change any policy considerations or economic investment trade-off decisions, but it notable for its positive findings.

The importance of the IQ question remains significant. IQ, both for individuals and in aggregate for a society, is strongly associated with positive life outcomes and overall productivity. If IQ is fixed, then there is some optimal expenditure of social investment in education which can be approximated and there is no point in investing more than that optimum. If, on the other hand, IQ can be increased, then there is some breakeven equation that can be derived. You are essentially purchasing extra IQ points in return for the expenditure of additional societal resources on education.

As a nation, we are expending nearly three times the real per capita resources on education as we did in 1970 but we have achieved no measurable increase in national IQ (standardized test scores). I believe this masks a real underlying improvement in that our current population is culturally, socially and linguistically much more heterogenous than in 1970. Just maintaining scores with that greater heterogeneity is an achievement. None-the-less it is hard to argue that there might not be some significant misallocation of social resources (see The Case Against Education by Bryan Caplan.)

Ritchie and Tucker-Drob's results aren't robust enough to refute that proposition but they are real enough to want to find out more.