2010-11: Gavin Bayreuther was the top scoring defensemen for the Holderness School while also playing soccer and lacrosse at the Plymouth, NH prep school. He scored 7 goals with 6 assists in 24 games for a Bulls team that finished 7-21-1.
2011-12: Bayreuther emerged as one of the top defensemen in New England prep hockey in his senior year as Holderness reached the championship game of the NEPSIHA small school division. He shared the Bulls' scoring lead with junior forward Tyler Mathieu, both finishing with 34 points. Bayreuther scored 14 goals, including a goal in the 3-2 overtime loss to Kimball Union in the championship game, and had 20 assists in 29 games. Bayreuther committed to playing college hockey at St. Lawrence in 2013-14 and was selected by Cedar Rapids in the second round (37th overall) of the 2012 USHL Entry Draft. He was ranked 186th amongst North American skaters in Central Scouting's final rankings but was not selected in the 2012 NHL Draft.
2012-13: Bayreuther began the season with Cedar Rapids before being acquired by Fargo in exchange for Notre Dame recruit Justin Wade in a swap of defensemen. In 60 USHL regular season games between the two teams he scored 9 goals with 24 assists and was +8 (+16 with Fargo in 41 games) with 43 penalty minutes. The Force finished second in the Western Conference and lost to Dubuque in the Clark Cup finals. Bayreuther scored 2 goals with 1 assist and was -1 with 14 penalty minutes in 13 playoff games.
2013-14: Bayreuther was the third-leading scorer amongst all NCAA defensemen in his freshman season at St. Lawrence. In 38 games he scored 9 goals with 27 assists and was +1 with 20 penalty minutes. The Saints finished eighth in ECAC Hockey and swept Brown in a first round series before falling to Colgate in the quarterfinals.