It's been demonstrated by controlled research that students who have teachers who expect them to perform better than their peers do, even when the expectations of the teachers are not founded on fact.
In the Oak School experiment discussed in this book teachers were led to believe that certain students, selected at random, were likely to be showing signs of a spurt in intellectual growth and development. The results were startling. At the end of the year, the students of whom the teaches had these expectations showed significantly greater gains in intellectual growth than did those in the control group.
The Jussim et al review of that literature is worth reading. Expectations do seem to have causal impact, but the effect is usually small relative to measures of past performance and ability, and teacher expectations tend to reflect past performance more.
The review covers some serious challenges to the effect sizes claimed by Rosenthal and coauthors, such as effect sizes declining with sample size and publication bias. Or, regarding the original Pygmalion/Oak School experiment:
...Snow (1995) also pointed out that the intelligence test used in Pygmalion was
Post will be returning in Main, after a rewrite by the company's writing staff. Citations Galore.