The second part of what you quoted disagrees, they don't agree the gap is closing. They make it explicit near the bottom: > The effect itself is strong and co

The second part of what you quoted disagrees, they don't agree the gap is closing. They make it explicit near the bottom: > The effect itself is strong and consistent, but we found no differential gender or race FE, nor was there much of a differential urbanization status identified. The positive finding of a differential FE in relation to maternal education (and at a smaller level, household income) at the older ages is suggestive of some of the dynamics of the process leading to the Flynn Effect. However, we do not consider our findings to be confirmatory in any sense.