In recessions, those who have the hardest time finding jobs are those who try for the first time. Facing these difficulties, many decide to pursue their studies in graduate school. From this, one should expect future productivity to be higher in the future, because of the higher level of human capital. But for a given level of human capital, labor productivity should be lower post-recession, because the marginal new graduate is of lower quality.
Michael Boehm and Martin Watzinger look at the performance of PhD economists and find that those who studied or graduated during a recession over-perform the others as measured by publication records. That would not surprise me for those who graduated during tough times, as only the best get jobs. Indeed, the study matches those who graduated with those who are still members of the American Economic Association. Thus, there is some selection bias. But for those who start in a recession, and thus would graduate in "normal" times, given the average length of a recession, this is more surprising. Boehm and Watzinger can justify this with the good old Roy model of reallocation of talent: in a recession, people switch to recession proof sectors, and those who can do this the most easily are those who are about to choose in which sector to work: students. As the number of graduate students slots does not change much, at least in Economics, the quality of those admitted is higher, if the admission officers do their work well. As the publication record many years later shows, they do.