Science labs are being installed on the second floor. On the first floor, repairmen are working in a hallway lined with paintings by Jackson Pollock and Winslow Homer to install a “smart board” for teachers to use in the classrooms. And in the recently waterproofed and sandblasted basement of the former St. William’s elementary school, dozens of students are on lunch break.

“Work is still being done,” says Jeffrey Thielman, the president of Cristo Rey Boston, the private Roman Catholic high school that has moved into the property, while conducting a brief tour of the new digs. “All these guys should be out of the building in a week.”

Short term needs remain: a chapel located next door to the cafeteria. Long term needs include fixing up the parking lot, further waterproofing, installing a new kitchen and ventilation system. “What we did was a maintenance job,” costing roughly a million dollars, he said. That included converting the gymnasium into a library, and adding several dozen computers and 7,000 books.

Residents of Savin Hill and the surrounding community will get a chance to see for themselves this Sunday at an open house that has been scheduled between 1 p.m. and 3 p.m.

Later that week, on Friday, Bishop Robert Hennessey will say a Mass for the school at Blessed Mother Teresa of Calcutta Church, with tours and a dedication to follow. Expected attendees include Mayor Thomas Menino, City Councillor Maureen Feeney, and Thomas P. O’Neill, chairman of the board of Cristo Rey and CEO of O’Neill and Associates.

Part of a national network of 22 schools in 19 cities called Cristo Rey and originally located in Cambridge, the school is looking to expand to 400 students from 280 this year, a gain of 20 over last year. The school finished fiscal year 2010 in the black, financially, after three years of losing a total of a million dollars. Seventeen teachers work there, and students participate in a work-study program that has them at some 70 Boston firms. Many commute by public transportation.

“I haven’t heard one complaint from the time they’ve been there,” said state Rep. Marty Walsh, a Dorchester Democrat who lives across the street from the school, on Tuttle St. “I think it’s going to be a win for the neighborhood. They’ve got an open-door policy, basically.”

The influx of students also gives a boost to the local economy, Walsh said. An ice cream shop is also due to open soon down the street.

The St. William’s property, once a parochial school that was combined with St. Margaret’s into one grammar school called Blessed Mother Teresa during the consolidation of Dorchester parishes, had been used largely as storage space before its sale to Cristo Rey.

“Most of the people are just thrilled; the grounds are looking better,” Fr. Jack Ahern, whose parish owned the property, said. “People are curious to see what repairs were made. People have spoken to me, and there have been quite a few. They are happy it’s a school again.”