President Obama prepares to catch a basketball thrown by team member Brooke Bohn and her project, a basketball catapult, while he hosts the 2014 White House Science Fair in the State Dining Room at the White House in Washington, May 27, 2014. REUTERS/Larry Downing

President Obama hosted what he called "one of my favorite events" Monday: the White House science fair.

It's the fourth time Obama has turned into the commander-in-geek for an hour or so, checking out projects from students around the country that far eclipse the baking soda and vinegar volcanoes and half-dead terrariums many of us made in our youth. Obama said their projects certainly eclipse anything he ever made. He said he "killed plants," as a student, and a bunch of mice once escaped from a science project into his grandmother's apartment. "There are no rodents loose in the White House," he told a group of students, their parents, teachers and others.

Instead, there were more than 100 students from 30 states who proudly displayed their projects in the State Dining Room, the Blue Room and the Red Room. This year there was a focus on girls and young women who are interested in science, technology, math and engineering -- known as STEM.

Obama spent nearly an hour talking to students about their projects and taking photos. He spoke with two teenagers from Natick, Mass., who invented a robot that would help search and rescue personnel find people trapped in icy bodies of water, caught a basketball tossed by a mechanical dummy and chatted with his "Chicago homies," two high schoolers who invented a robot that can hurl things. "Where do I buy stock in you?" Obama asked a Florida student who invented a reusable sandbag that expands when it gets wet.

All the fun had a purpose -- the administration announced a new $35 million competition to train science, technology, math, science and engineering teachers, an expansion of a program to provide low-income students STEM learning opportunities and a STEM mentoring project.

Yes, most people were excited to meet the president. But one man got even more of a rock star reception: Bill Nye the Science Guy, who spent a good half hour posing for pictures with fans. Also garnering some attention? "Mohawk Guy," a NASA flight engineer whose spiked, stars and stripe haircut gained a cult following.