WE’VE all been there: you feel especially smart and funny when talking to a particular person, only to feel hopelessly unintelligent and inarticulate in the presence of another.

You’re not imagining things. Experiments show that when people report feeling comfortable with a conversational partner, they are judged by those partners and by observers as actually being more witty.

It’s just one example of the powerful influence that social factors can have on intelligence. As parents, teachers and students settle into the school year, this work should prompt us to think about intelligence not as a “lump of something that’s in our heads,” as the psychologist Joshua Aronson puts it, but as “a transaction among people.”

Mr. Aronson, an associate professor at New York University, has been a leader in investigating the effects of social forces on academic achievement. Along with the psychologist Claude Steele, he identified the phenomenon known as “stereotype threat.” Members of groups believed to be academically inferior — African-American and Latino students enrolled in college, or female students in math and science courses — score much lower on tests when reminded beforehand of their race or gender.