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The Pygmalion effect, named for the Greek sculptor whose statue came to life, holds that high expectations raise performance and low ones lower it. The episode opens with Clever Hans, the Berlin horse that seemed to do arithmetic by tapping a hoof but was actually reading the tension and relief of his audience. In 1968 Robert Rosenthal and Lenore Jacobson gave students at a California elementary school a supposed test of latent potential, then told teachers that a random 20 percent were intellectual bloomers. At year’s end first and second graders on the list showed significant IQ gains, which Rosenthal attributed to subtle changes in how teachers treated them, described in the book Pygmalion in the Classroom.

Robert L. Thorndike attacked the baseline test, noting one regular class averaged in the mentally disabled range, and quoted a colleague: if a clock strikes 13, doubt every chime before it. A meta-analysis by Stephen Raudenbush found the effect fell to nearly zero if teachers had known students for two weeks, and a 2005 review of 35 years of studies found classroom effects weak, touching perhaps 5 to 10 percent of students. The stronger evidence came from adults. In 1982 Dov Eden and Abraham Shani told Israel Defense Forces instructors that random trainees had high leadership potential, and those trainees outperformed on four objective tests. Eden later described a Pygmalion leadership style and, with Ravid, a Galatea effect from raising people’s expectations of themselves.

• In a 1969 study by Jenkins and Deno, teachers rated their own teaching higher when students were secretly told to act attentive.
• Nursing home patients expected to progress quickly showed lower depression and fewer acute hospitalizations.
• Alcohol-dependent clients arbitrarily labeled motivated dropped out of therapy less often.
• Researchers warn that labeling employees high potential by fiat risks destroying trust if discovered.
• Studies by King in 1970 and by Sutton and Woodman in retail found no Pygmalion effect among female subordinates.