The study’s author, Simon Bensnes, a Ph.D. candidate in the Department of Economics at the Norwegian University of Science and Technology, combined these with pollen count data linked to the location and time at which each student took each exam, as well as other demographic and air-quality data used to control for potentially confounding factors.

Pollen counts are measured in grains of pollen per cubic meter of air and can be as high as the 100s at the height of pollen season in Norway. For students allergic to pollen, Mr. Bensnes found that a pollen count increase of 37 — large enough to cause symptoms in highly allergic people — is associated with a drop of about one-tenth of a point in exam scores. The scores range from one (worst performance) to six (best performance).

Does such a seemingly small effect matter in the long run? Other results suggest they do. The study also finds that higher pollen counts correlate with a slightly lower likelihood of enrolling in a university and a lower probability of going into a STEM field. However, though the statistical methods to analyze test scores are rigorous enough to reasonably infer they’re causal, the ones for these longer-term results are less so.

Still, Mr. Bensnes said, “it would be surprising if there were no effects in the longer run.” This is particularly likely in countries where exams are weighed more heavily than in Norway toward entrance to institutions of higher education. There, exams count only for about 15 percent of entrance determinations.

Norway is not the only setting where a pollen-exam relationship has been found. In Britain, students take an exit exam at the end of secondary education in the spring or summer, when pollen counts are high. They also take a practice test the prior winter. Researchers found that compared with those with no allergy symptoms, British students who report allergies or take allergy medications during their secondary education exit exams are 40 percent to 70 percent more likely to score a full grade lower than they did on their practice test.