Complex sentence: With Norman Howard's retirement, David W. Gow became headmaster, and during the period of his leadership a vigorous building and academic development program was undertaken, with the school growing from about 116 students to over 150.
Split into simpler sentences: With Norman Howard's retirement, David W. Gow became headmaster. During the period of his leadership, a vigorous building and academic development program was undertaken, with the school growing from about 116 students to over 150.