"He was the best math teacher I've ever run into," said William Zylinski, district supervisor and former principal at Lacey.
But Geiger, 39, is also one of the best soccer referees. His experience includes the 2011 Under-20 World Cup final in Colombia, the 2012 Olympics in London, and 11 years in Major League Soccer. MLS named him referee of the year in 2011.
In 2012, when the Professional Referee Organization offered Geiger a full-time, salaried officiating position that would give him a realistic shot at the 2014 World Cup, Geiger had to make a difficult decision. Taking the job would mean leaving teaching, choosing one passion over another.
"He didn't want to go," said Steven Geiger, Mark's brother, who also teaches math at Lacey. "But once the PRO started and he had that opportunity, he knew if he wanted to get to [the World Cup] he couldn't do both things."
Mark Geiger, who was not allowed to speak to the media while working at the World Cup, ultimately took the officiating job and left Lacey in January 2013. The tough choice paid off: A year later, FIFA picked Geiger as one of 25 elite referees from around the globe - and the only one from the United States - to referee at the World Cup in Brazil.
The referees, like the teams, advance at the World Cup by performing well. Each official is guaranteed only one game, and in the end, only one center referee is left standing to manage the World Cup final. No American has made it out of World Cup group stages as a center referee.
Geiger worked the Group C opener between Colombia and Greece along with Wednesday's Group B match. After two solid matches with no controversy, he might have a shot at the World Cup final.
"That was good refereeing," said Ian Darke, ESPN's play-by-play man for the game, when Geiger awarded a free kick to Chile in the 44th minute. The free kick resulted in the game's second goal, when Chile's Charles Aranguiz knocked in a rebound.
Grant Wahl, a senior writer at Sports Illustrated, commended Geiger in a Twitter post.
"US referee Mark Geiger with more good work in Chile-Spain," Wahl said. "FIFA gave him U-20 World Cup final in 2011. Would they give him a WC final?"