Don is an active Masters athlete in both cycling and running. He enjoys competing on the track and on the road in both sports, but finds the fall cyclocross and cross country seasons connect him most to nature in New England. Don has been coaching endurance athletes part-time since 2015. Recently retired from more than 40 years in the agriculture, nursery, and landscape industry, he is now focusing more time on coaching and mentoring athletes. Don has earned licenses and certificates through USATF, USAC, TrueSport, SafeSport, CoachTrue, and NFHS. Six children have given him a lifetime of experience in teaching, caring, and making adjustments.

Don’s goals as a coach are to foster awareness and appreciation of skills and opportunities as individuals, as a team, and as a community; to help our athletes achieve personal successes progressively and safely; and to establish positive lifetime practices through sport.

David Lyons has coached the St. Mark's cross country team since 2005. Over that time, the team has enjoyed considerable success at both the varsity and junior varsity levels.

Both teams have had winning records every year for more than a decade. The varsity's regular-season record since 2005 has been 149 wins against only 41 losses. The JV's record has been even better: 168 wins and 23 losses. The varsity won ISL and New England Championships in 2011 and 2013, as well as additional New England Championships in 2006 and 2007 (and second place finishes in 2008, 2009, and 2010). Last year, the team finished second in the sixteen-team ISL. The JV won ISL titles in 2015 and 2016, as well as New England Championships every season from 2006 to 2009 (finishing second in 2005 and 2010). St. Mark's also has had a number of runners recently go on to compete in college at schools like Colby, Hamilton, Connecticut College, Lewis and Clark, Kenyon, and Hobart.

David Lyons came to St. Mark's after practicing labor and employment law at Ropes & Gray in Boston, clerking for Judge Bruce M. Selya on the U. S. First Circuit Court of Appeals, and teaching history at St. Andrew's School in Middletown, Delaware. He graduated from the University of Virginia (JD, MA) and Harvard (BA), where he lettered in baseball and played on the freshman football team. He has taught a variety of courses at St. Mark's (most recently Advanced American History, Advanced American Government, AP European History, and The Atlantic World).

Nathan Argueta is the Assistant Director of Financial Aid and Associate Director of Admission. Nathan is coming from his alma mater Nativity Preparatory School New Bedford where he has served as the Dean of Instruction for the past two years. In this role, he prioritized re-envisioning the school's curriculum and instructional coaching & development as a means of pushing the school towards becoming an anti-racist institution. Nathan earned a Bachelor of Arts in English (with a minor in Film and Media Studies) from Davidson College. He has also served as the Assistant Director of Admission at New Hampton School. Nathan helps St. Mark's fill the halls with a diverse student-body committed to leadership and service. Nathan lives on campus, and in his free time, he enjoys going on long runs and salivating over sneaker-drops he'll never actually win.