Members of a building commission were sworn in this month to oversee the renovation and expansion of the Devotion School, the next in a long line of K-8 schools being readied for an increase in the town’s student population. Most of the commission’s work will start in the fall, according to Board of Selectmen chairwoman Betsy DeWitt, who is a member of the new panel. During the summer, the school system will determine what programs might be moved and whether Devotion — built to accommodate three classrooms per grade — will instead hold four, five, or six, and whether the Harvard Street site, which also includes a home dating from the Colonial period, has enough space for those extra classrooms. The schools have seen unprecedented growth in the elementary grades over the last six years, and in the fall may see 650 kindergartners — up from 390  seven years ago. “The trick is to manage for this peak population without overbuilding,” DeWitt said.