Born and raised in the Bakersfield-Wasco area and a 1956 Wasco High graduate, Thiessen began his teaching and coaching career at Fowler High in 1961, where his boys' tennis team went 45-6 in four seasons. Thiessen then moved to Wasco High where he coached boys tennis from 1965-2003, posting a 622-124-3 record with 10 Central Section titles. Thiessen moved to Bakersfield Christian for the 2003-04 school year where he continues to coach boys and girls tennis and girl's basketball. Through the fall of 2017, the BCHS boys' tennis team has a 262-50-2 record with 11 section titles during his tenure with the girl's tennis team 301-49-2 with 13 straight section titles. He is in his second stint as the girls' basketball head coach and led the Eagles to a Central Section title in 2006. Thiessen has served as the CIF Central Section's tennis advisory committee chairman since 1965. In addition to coaching, Thiessen has taught math and biology and served as a counselor. As a youngster, Thiessen was a ranked junior player for the USTA Southern California Organization.