Mann played on the water polo team at Corona del Mar High School and won three C.I.F.

Starting his sophomore season, Mann began to rapidly develop as a top youth player in the country and was selected to train with the United States Olympic team shortly after his Sophomore year at Corona del Mar High.

Throughout his career at CdM, Mann was named Orange County player of the year multiple times.

While at CdM Mann was a three-time First team All-America and was known for his goals scoring ability both in the center and on the perimeter, as a senior, he scored 109 goals and was named the Orange County Player of the Year despite missing the first month of the season due to an injury sustained in international competition in Russia.

[2] In 2006, Mann scored a team-leading 80 goals and led California to the NCAA Championship.

[3] He was a first team All-American for the third straight year and also won the Peter J. Cutino Award as the nation's best male collegiate water polo player.

This success further solidified Mann as one of the most accomplished and sought after U.S. players in the International Professional league system.