GMG, and Garwin HS before it, also have a rich boys' basketball tradition. Garwin won many conference titles and made two runs to the Iowa State Basketball Tournament. Garwin first made the 1978 Class 1A State Tournament, losing to Lake View-Auburn 54–44. They also made it to the 1983 Class 1A Championship Game, losing to Palmer 61–55. Garwin/GMG was long coached by Gary Peterson, who over his 33 years as head coach, amassed a record of 478 wins and 216 losses, which ranks him 34th all time in Iowa boys' basketball history.