Mr. Costello began his career in 1974 teaching elementary school, and taught all self-contained subjects on that level. He moved to New York Military Academy in 1978 where he taught English, Latin and Social Studies. From 1983-2001 Mr. Costello was Headmaster of New York Military Academy for grades 5-12 and PG. He taught and was the Assistant Principal of St. Thomas School in 2001, becoming its Principal from 2007-2011. Mr. Costello has been teaching at The Storm King School since 2012.