Grace Cotter Regan has started serving as the new head of school for the sixth to 12th grades at St. Mary’s High School on Tremont Street.  Regan was named in March  by the St. Mary’s board to succeed Raymond A. Bastarache,  who retired June 30.  Regan, of West Roxbury, has nearly 30 years of experience working in education and institutional advancement, including 23 years  at Catholic institutions. Most recently, from 2005  until assuming her new job, she had served as executive director of advancement for the New England Province of Jesuits.  She is also a partner in Partners in Mission,  a Westwood-based consulting firm focused on developing excellence in advancement and leadership in Catholic schools, dioceses, religious congregations, and parishes.