Prior to joining Schalmont, he spent almost 10 years in the New York State Education Department. While there, he was first an associate in school business management and later the acting supervisor of Educational Management Services. From 1979 to 1987, Kellet was the business administrator of Sodus Central School District in Sodus, NY. He spent two years prior to that as the business administrator for Northeastern Clinton Central School District in Champlain, NY. From 1972 to 1974, he taught classics at Hotchkiss School in Lakeville, CT.

In 1971, Kellet received a Bachelor of Arts degree from Union College, graduating cum laude with a distinction in classics. He later received a Master of Business Administration degree from SUNY Albany in 1977. He also received permanent school district administrator (SDA), school district leader (SDL), Latin, and business certification from the NYS Education Department.

His current professional memberships include the NYS Association of School Business Officials, where he serves as curriculum director for the annual summer business management workshop.

Kellet and his wife have three grown children.