MARINE ON ST. CROIX, Minn.  From the hallway, Abby Brown’s sixth-grade classroom in a little school here about an hour northeast of Minneapolis has the look of the usual one, with an American flag up front and children’s colorful artwork decorating the walls.

But inside, an experiment is going on that makes it among the more unorthodox public school classrooms in the country, and pupils are being studied as much as they are studying. Unlike children almost everywhere, those in Ms. Brown’s class do not have to sit and be still. Quite the contrary, they may stand and fidget all class long if they want.

And they do.

On one recent morning, while 11-year-old Nick Raboin had his eye on his math problems, Ms. Brown was noticing that he preferred to shift his weight from one foot to the other as he figured out his fractions. She also knew that his classmate Roxy Cotter liked to stand more than sit. And Brett Leick is inclined to lean on a high stool and swing his right foot under a desk that is near chest level. Helps with concentration, he and Ms. Brown say.

The children in Ms. Brown’s class, and in some others at Marine Elementary School and additional schools nearby, are using a type of adjustable-height school desk, allowing pupils to stand while they work, that Ms. Brown designed with the help of a local ergonomic furniture company two years ago. The stand-up desk’s popularity with children and teachers spread by word of mouth from this small town to schools in Wisconsin, across the St. Croix River. Now orders for the desks are being filled for districts from North Carolina to California.