The woods near the German town of Idstein, north of Frankfurt, are the home of one of the country's about 700 Waldkindergärten, or "forest kindergartens," in which children aged three to six spend their weekdays outside year-round, come rain or snow.

In environmentally conscious and consumption-wary Germany, the Waldkindergärten are a throwback to the philosophies of Friedrich Fröbel, the German educator who opened the world's first kindergarten more than 150 years ago. He counseled that playing in nature, rather than focusing on letters or numbers, was best for young children.

At left, one of the Idstein kindergarteners occupies herself with a stick and a puddle.

Academic studies on the pros and cons of such schools are in their infancy, but some researchers believe Waldkindergarten students exercise their imaginations more than their brick-and-mortar peers. Despite dangers from parasite-bearing insects, they also appear to get sick less often, a benefit of all the fresh air.

At left, two Idstein students in their school's "Platz der Stille," or "Place of Tranquility."

The teachers, 50-year-old Ulrike Schnaar, left, and Margit Kluge, 51, right, escort their students into the woods each morning. There, the children sing songs, jump in puddles and get comfortable with nature. Climbing trees – or clambering atop a makeshift teepee -- is a popular activity.

The children rarely ask for toys, their teachers say, and usually improvise with what the woods offer. At left, one student whittles a stick with a knife. "I'm making a lance," she explained.

Ms. Kluge, the teacher, says there haven't been any bad accidents beyond the occasional scrapes and bruises.

The class's woody setting makes for some unusual furniture.

The children and their teachers -- who come to school dressed to spend the full day outside -- relax in the "wald sofa," a ring of tree stumps and twigs. "There is no bad weather, just bad clothing decisions," says Ms. Schnaar.

The Waldkindergarten has a trailer that serves as a refuge if the weather gets too stormy but the children hardly ever set foot in it. Large letters on the trailer's wall read "Zauberwald," or "Enchanted Forest."

The facilities even include real "coat trees."

The Waldkindergarten forest includes lots of decorative wood carvings, like these mushrooms.

The children contribute to the decorations. Just before Easter, the children busied themselves painting Easter eggs.

Sweets are discouraged in the children's late-morning snacktime; on a recent day, their teachers explained the life-cycle of toads while they ate.

Around 1 p.m., the children gather to sing a final song before leaving the forest, taking some mud along with them.