Scrawling measurements on a cedar fence post, fifth-graders Cassidy French and Bella Solari, both 11, were using a ruler to make sure each line was perfect.
"That's about right," Bella said.
The pair matched the bottom of their boards together to check their work before they took them over to parent volunteers who manned the power saws.
Their birdhouses were finally ready for assembly.
For Bella, and several of her classmates, this was their first time building something square from a single piece of wood, and so she was being extra careful.
"If you don't get it right, it will be all crooked," Cassidy warned.
Getting measurements correct before they assemble them was a crucial lesson that fifth-grade teachers Rob Barthule and Ryan Truscott emphasized before they began on Tuesday.
"We went over that this morning," Barthule said. "You get one shot. You better measure twice and cut once."
This is the second year that the 45 students in fifth grade at Boulder built birdhouses.
"Part of our Common Core (curriculum) is measurement and using measurement," Truscott said.
The two teachers have spent their last math unit teaching students to measure inches as well as centimeters.
"We were learning to measure within fractions of an inch," Barthule.
Making the birdhouses is the culminating project. It's not only fun, it's putting skills into practice.
"They can actually see a project come to life," he said. "It's practical application."
Scott Young, the grandfather of fifth-grader Saige Christianson, said he was having a great time teaching his granddaughter about construction.
"She is the best hammerer I've seen," he said. "She's only hit my thumb once."
The project was not only beneficial in teaching basic construction skills, it was also a chance to employ classroom lessons in the real world.
"It comes into everyday practical life," he said. "It's something that we use every day."