There is every reason to be skeptical of these findings. Like magic spells cast by a modern-day Merlin, they sound much too good to be true. Why should brief interventions carry so much punch when more intricate and costly strategies — everything from summer school to single-sex education — are often less effective?

Innovative social-psychological thinking, not magic, is at work here. These interventions focus on how kids, hunched over their desks in the back of the classroom, make sense of themselves and their environment. They can be brief but powerful because they concentrate on a single core belief.

There are three strategies represented here. The first, pioneered by the Stanford social psychology professor Carol Dweck and illustrated by the initial example, aims to change students’ mind-sets by showing them that their intelligence can grow through deliberate work. I’ve written about Dr. Dweck’s theories as applied to college students, but they are just as successful with students in middle school.

The second uses constructive critical feedback to instill trust in minority adolescents, a demonstrably powerful way to advance their social and intellectual development.

The third intervention — and in some ways, the most powerful — invites students to acknowledge their self-worth, combating the corrosive effects of racial stereotypes, by having them focus on a self-affirming value.

These interventions are designed to combat students’ negative feelings. I’m dumb, some believe; I don’t belong here; the school views me only as a member of an unintelligent group. The first two experiences give students the insight that brain work will make them smarter. The third invites them to situate themselves on the path to belonging or to connect with their values in a classroom setting. The goals are to build up their resilience and prepare them for adversity.

The impact, in all these studies, is greatest on black and Latino students. That makes sense, since as adolescents they are far more inclined to see teachers as prejudiced and school as a hostile environment. As these youths come to feel more secure, they are likely to make a greater effort. Success begets success. They start earning A’s and B’s instead of C’s, they take tougher classes and connect more readily with like-minded students.