The Center School is opening this month after an extensive rehabilitation and expansion to help accommodate a growing student population at the elementary school. An open house for parents of kindergartners is set for Monday from 6:30 to 7 p.m., while parents of students in grades 1 to 5 had a curriculum presentation on Wednesday, according to a posting on the school’s website, center.nrsd.net. The total cost of the project, approved by Town Meeting in 2009, was $35.6 million.