Waynflete School is proposing a major renovation and expansion project at its campus in Portland’s West End.

The private prep school wants to replace old buildings that are too small for the school’s current needs, school officials said.

The $12 million investment in the school on Spring Street will include demolishing part of the Lower School, which serves students from pre-kindergarten to fifth grade, and razing the gymnasium to replace it with a new one. The project would double the size of the Lower School, from 20,000 square feet to 40,000 square feet of instructional space.

“This would be the largest construction and renovation project in the school’s history,” said Geoffrey Wagg, head of school.

Waynflete was founded in 1898 and occupies 5 acres in one of the city’s most exclusive neighborhoods. Its long-term development plans have been watched closely by many residents in the historic and densely developed West End.

Students walk down Storer Street next to the Waynflete School campus Friday. Waynflete plans “the largest construction and renovation project in the school’s history.” Whitney Hayward/Staff Photographer

In 2010, the Portland City Council rejected parts of a more extensive Waynflete expansion plan that was opposed by some neighbors. That plan would have allowed the school to buy adjacent houses and convert them into school buildings, a proposal that some West Enders called “institutional creep” and a threat to the character of their neighborhood.

However, the council at the time approved construction projects within the existing campus as part of what was described as a 20-year plan for the school.

The latest proposal for the school was posted on the city’s website Friday, and will go before the Planning Board in the coming months.

If the plans are approved, construction of the project likely would begin in June 2017 and be completed in time for the start of the 2018-19 school year, Wagg said.

Heather Lippert walks past the Waynflete gymnasium Friday. The private school occupies 5 acres in one of Portland’s most exclusive neighborhoods. Its long-term development plans have been watched closely by many residents in the West End. Whitney Hayward/Staff Photographer

“We have a very experiential program,” he said. “We don’t have students sitting in rows and the teacher at the front of the room. The kids are actively learning all day. But we don’t have enough space and we’re always moving things around. The new building would allow us to offer all of our programs without the logistical problems.”

Tuition at Waynflete costs $24,000 to $29,000 per year, depending on the grade of the student, according to the Waynflete website. The school has about 550 students from pre-kindergarten through high school.

The L-shaped Lower School is actually two separate buildings joined together, Wagg said. The older part, a historic building constructed more than 100 years ago, will be renovated, while the newer section, which was built in the 1960s, will be torn down and replaced. The historic building was originally a stable, and was converted to classrooms in 1912.

The new Lower School will be constructed using environmentally friendly, sustainable methods incorporating abundant insulation, use of natural light and renewable energy sources, Wagg said.

Meanwhile, the new gymnasium would replace one built in the 1970s that’s being used by grades K-12 and is far too small, he said. The size of the gym would increase from 9,300 square feet to 13,600 square feet, according to city planning documents.

Construction of the new Lower School and gymnasium will be mostly within the buildings’ existing footprint, Wagg said.

Ian Jacob, president of the West End Neighborhood Association, said it’s the first he’s heard of the plans. The neighborhood group would be examining the plans and “looking forward to community involvement in the process,” he said.