New research published today in Nature shows that IQ changes are correlated in physical changes in the adolescent brain.
"We found a considerable amount of change in how our subjects performed on the IQ tests in 2008 compared to four years earlier," explains Sue Ramsden, first author of the study. "Some subjects performed markedly better but some performed considerably worse. We found a clear correlation between this change in performance and changes in the structure of their brains and so can say with some certainty that these changes in IQ are real."
Sara Sparks of Education Week's Inside School Research blog has the rundown