DORCHESTER -- Approximately 150 volunteer workers representing eight organizations put in a full day of work April 24 preparing the former Saint William’s School in Dorchester for the August arrival of nearly 300 students at the new home of Cristo Rey Boston High School.

Cristo Rey serves low-income students, primarily from Boston neighborhoods and is part of the Cristo Rey Network, an association of 24 college preparatory schools across the country. The school has outgrown its current location at North Cambridge Catholic High School, and will change its name to Cristo Rey Boston High as of the next school year.

The project was the largest of a total of eight property renovations performed that day under the overall direction of Rebuilding Together Boston (RTB) as part of National Rebuilding Day.

RTB is an affiliate of Rebuilding Together, a national non-profit organization that works to preserve affordable homeownership stock and revitalize communities at no cost to those in need. This year, National Rebuilding Day involved 200 affiliates bringing in more than 250,000 volunteers nationally to repair and restore more than 4,000 homes and non-profit facilities.

At the Cristo Rey site on Savin Hill Avenue, workers renovated 11 classrooms, scraped and painted the encircling wrought-iron fence, refinished the school’s two main doors, and cleaned up the building’s exterior.

“We are determined to preserve the original beauty of the school. It is a wonderful building,” said the school’s principal Father Jose Medina, who also pointed out that the school’s first-floor auditorium and basketball court would be subdivided into a library/arts center and assembly hall.

Fidelity Investments, now in its ninth year of working on National Rebuilding Day, was the project’s lead sponsor. Veronica Johnson-Eghan of Fidelity directed the volunteers on the site. The site captain and project supervisor was Matt Awad, an executive of the Gilbane Building Company.

Other organizations that sent volunteers to work at Cristo Rey included the Alpha Sigma Nu, the national Jesuit honor society, from Boston College; Shake the Tree; Wentworth Institute; Tech Target; On Force; and Blue Cross Blue Shield.