Boston, MA 11/22/11 A class enjoys the indoor pool. Jeichael K. Henderson (cq), principal of the John P. Holland School, gives The Boston Globe a tour, on Tuesday, November 22, 2011. The Dorchester school has a number of facility perks and is making changes to improve its academic programs. (Pat Greenhouse/Globe Staff); Reporter: Vaznis; Section: Metro; Slug: XXX