Swimming for Rockhurst all four years of high school, Thomas helped lead his team to their first ever gold medal (200 medley relay) and first state title in 2005. In the same year, Thomas was Rockhurst's first swimmer to win an individual gold medal, winning by just three one-hundredths of a second in the 100 back. As captain of his team in 2006, he guided his team to the first ever back to back Missouri state titles by a Kansas City school.

His long memory of high school swimming will always be anchoring the 400 free relay against number two seed rival Blue Springs, a race which decided the 2005 Missouri State Championships.

At the EISL Championships his freshman year, Thomas placed 7th in the 200 back, thirteenth in the 100 fly, and ninth in the 100 back. He also swam on the 200 free relay.