The building St. Croix Preparatory Academy is close to putting up in Baytown Township might be the most ambitious building project ever undertaken by a charter school in Minnesota.

The 350-student school received approval from the Baytown Township Board of Supervisors this week to build a $19 million, 140,000-square-foot building off Stagecoach Trail. If the school gets approval from Washington County on Jan. 22, it could break ground by late spring and open in fall 2009.

"What's different about us is, you don't see a K-12 school very often. It's a little ambitious, but we think we have the growth model to sustain it," executive director Jon Gutierrez said.

Plans call for the building to have 39 classrooms, a gymnasium, media center, theater, outdoor amphitheater, two baseball fields, a soccer field, a full-size track and space to add a swimming pool later.

It would allow the school to accept some of the 400 students on its waiting list; St. Croix Prep's plan is to open the new building with 650 students and grow to a full enrollment of 975.

It currently has students from kindergarten to 10th grade, but it will add 11th and 12th grades over the next two years.

Plans call for three 25-student sections in each grade and no more than 75 students in a graduating class. Gutierrez said St. Croix Prep would eventually increase its staff from 50 to 60.

The school, which opened in 2004, had pursued sites around Stillwater but has never progressed this far in its building plans.

"I'm speechless," St. Croix Prep school board member Carroll Davis-Johnson said. "It's taken a long time to get to this point."

What separates this plan from most of the roughly 130 charter schools in the state is its scope. St. Croix Prep would be the state's second-biggest charter school if it reaches its target enrollment. The new building would have segregated spaces that minimize interaction between elementary school and high school students.

The building would also allow the school's extracurricular activities to expand past the point most charters can accommodate in rented space, and Gutierrez said it sends a message that St. Croix Prep is here to stay.

"People want the whole product," Gutierrez said. "The minute you have a facility, you've got the whole product."

The school might have to have the whole product in order to stay afloat, since its mortgage payments will come from per-pupil state aid given to charter schools to make up for the fact they cannot ask taxpayers for support.

But Gutierrez pointed to the school's waiting list and its 95-percent student retention rate as reasons for optimism.

"It gives you some confidence," he said. "You always have that waiting list for revenue consistency."

Ben Goessling • 651-298-1546