To measure this “Pygmalion effect”, the researchers provided 11 teachers with a standardized English test and asked them to evaluate their 5th grade students’ reading comprehension, grammar, and writing abilities.
Meanwhile, students were given questionnaires to measure their academic self-concept and motivation, as well as their perceived teacher treatment.
One year later, the study was repeated, with the students now in 6th grade; and what the researchers found was that, after controlling for achievement and motivation in grade 5, teacher judgement still predicted motivation and academic achievement in grade 6.
Moreover, perceived teacher treatment and academic self-concept correlated, and mediated the relation between teacher judgment, motivation and achievement.
In a nutshell, "Students who were judged favorably set themselves challenging goals for future achievement because they believed that they could achieve them."
Source: Zhu et alia (2017)