PORTLAND — What was once Maine’s only all-boys Roman Catholic school expects 25 to 30 girls to sign up for classes this fall — the first time girls have been allowed to enroll.

Cheverus High School is undergoing an expansion this summer in preparation for the switch.

The 84-year-old school has 425 students enrolled — up from 395 last year — and the school expects to double enrollment over the next seven years, said Jim Crocker, Cheverus’ director of alumni relations.

“When the economy is good,” Crocker said, “private education becomes popular. Most people think sending your son and daughter to private school gives them the edge to get into a good college and have a better life.”

To prepare for enrollment increases, the school has completed a 49,500-square-foot soccer field and added 122 parking spaces. The school also added five classrooms, including a science classroom.

The school also received permission from the city to add a new gym, kitchen and cafeteria.