School not only gives students specific skills, it also increases their intelligence. One year of formal schooling between age 10 and 20 raises an individual's IQ score by 2.9 to 3.5 points, on average, say Torberg Falch of the Norwegian University of Science and Technology and Sofia Sandgren Massih of Uppsala University in Sweden. So 4 to 5 additional years of schooling increases IQ scores by about one standard deviation, a sizable effect, the authors say.

  Source: The Effect of Education on Cognitive Ability