A school principal spent a frigid night on the roof of Harrington Park School in Harrington Park, New Jersey, after students met his challenge to read 10,000 books months before he expected them to. The school has about 700 students in kindergarten through eighth grade.

Davies had agreed to let them choose their reward. They decided to shave the school's "HP" logo in his hair and send him on a rooftop camping excursion.

Davies, 40, headed up after school ended Thursday with a tent, a sleeping bag and other winter gear.

"I knew it would be cold," he said afterward. "But I didn't know it would be that cold."

Temperatures plunged into the 20s (below zero Celsius) Thursday night and Friday morning in northern New Jersey, according to the National Weather Service. Still, Davies -- somewhat steeled by several years of living in Montana -- said he managed to get a few hours of sleep.

Students and their families bestowed him with hot chocolate and other goodies. Some stopped by with kind wishes into the night and early in the morning.

"I felt so bad. I was out there this morning with, like, tons of jackets on, and he was up there with a tent," said Mary Wyley, a sixth grader.

As he thawed out, Davies said the chill was worth it.

"The students were so excited by the whole thing, and if it encourages them to read, then I would do it all again," he said. "Just not tonight."