Professor Flashman has preferred to follow a career in mathematics and has been actively involved in teaching calculus since beginning his graduate work. He had taught at Mount Holyoke College, Baruch College of CUNY, and Bard College before coming to his current position at Humboldt State University where he is Professor of Mathematics. He has taught summers at the University of California, Berkeley, and the University of San Francisco, and has been a Visiting Fellow at Yale University and a Visiting Professor at the University of Toronto in Canada.

For many years Professor Flashman has been working on a draft of the Sensible Calculus Book. He was book and media editor for UME TRENDS in which he wrote the column "Noteworthy Books and Such" until it ceased publication in 1996, and was a member the MAA committee on Calculus Reform And The First Two Years (CRAFTY) for 6 years ending in January, 1999.

His hobbies include music, tennis, chess, go, and trying to be on time.