Teacher expectations alone can dramatically raise a student's IQ.

In the famous 'Pygmalion in the classroom' study, teachers were told certain randomly chosen pupils were 'bloomers' poised to surge; those children then showed larger IQ gains, apparently created by expectation alone. It became a cornerstone belief about self-fulfilling prophecies.

A careful review by Jussim & Harber (2005) concluded that expectancy effects are real but usually small, sometimes fade, and occasionally even self-correct — and that the original study's largest effects were concentrated in a few younger grades and were statistically fragile. Expectations matter at the margins, especially for stigmatised or younger students, but they do not rewrite ability; the dramatic version of the Pygmalion claim is not supported.