Complex sentence: Gardner Dunnan, Avenues academic dean, headed the Dalton School for 23 years and most recently led the development of The School at Columbia, a K-8 school for children of Columbia faculty and the Columbia neighborhood.
Split into simpler sentences: Gardner Dunnan, Avenues academic dean, headed the Dalton School for 23 years. Most recently, he led the development of The School at Columbia, a K-8 school for children of Columbia faculty and the Columbia neighborhood.