Mr. Nottingham, the founder and executive director of The Challenging Learning Group, an education company, said: “My purpose is, instead of giving them clarity, it’s creating confusion, or cognitive wobble. Like when you are learning to ride a bike and it wobbles — I am trying to create that mental wobble so they have to think about it more.”

Mr. Nottingham identified three mental states that students occupy when learning something new: relatively comfortable, relatively uncomfortable and panicked. Too many parents and educators intervene when learning gets uncomfortable, denying students a chance to stretch enough to deepen their learning, he said. “It’s counterproductive,” he said, like trying to help a child learn to ride a bike by holding onto the back of the seat to navigate every bump, hole or obstacle.

In 2018, TNTP, a nonprofit based in New York focused on improving K-12 education, surveyed 1,000 lessons in five diverse schools to see why so many students were graduating with decent grades but were unprepared for college. It found that in class, students successfully completed most (71 percent) of the work sheets, class activities and other work they were given to do. But those assignments were too easy; they reflected grade-level standards only 17 percent of the time. “That gap exists because so few assignments actually gave students a chance to demonstrate grade-level mastery,” the authors of the survey concluded.

Not stretching students — because there isn’t time for the kinds of conversations that make learning interesting and, at times, tricky — can be consequential, especially for marginalized students. Lacey Robinson, president and chief executive of UnboundED, an organization that designs learning to be rigorous and meaningful, said educators sometimes did not have the content knowledge and training to help fill in gaps, and too often had low expectations for Black and brown students. This can cause those students to lose interest in learning; they get relegated to lower-level material and fall further behind.

“We often find that educators use what I call this really illogical model of putting students in a grade level below,” Ms. Robinson said, “in the hope that they catch up to the grade level they’re supposed to be in.”

“Your academic identity gets solidified the more you work that muscle,” she added. “And you work that muscle due to the rigor and the productive struggle.”

Some researchers have gone beyond encouraging struggle to actually design for failure. Manu Kapur, an educational psychologist at ETH Zurich, has spent 17 years showing that students learn new concepts more fully, and retain the knowledge longer, when they engage in what he calls “productive failure” — grappling with a problem before getting instruction on exactly how to do it.