It is, almost everyone agrees, a great way to earn college credits for free.

But the popular “College in the Schools” program, which allows Minnesota high school students to take college courses at their home schools, is facing some potentially costly changes. And some fear it will be tougher for some high schools, especially in rural districts, to keep offering the classes.

A new credentialing rule, scheduled to kick in next fall, could force hundreds of high school teachers to stop teaching the courses because they lack a master’s degree.

And the cost is going up for many school districts. The fees they pay to the Minnesota State college and university system, which sponsors most of these dual-credit courses, are slated to increase — in some cases double — over the next five years.

The net effect, says Joe Nathan of the Center for School Change, is a double whammy that will backfire on students.

“There will be fewer concurrent enrollment courses offered,” he warns, “and the classes themselves will cost many high schools much more money.”

The program itself has only grown in popularity. Since 2007, the number of students in the classes, where they earn high school and college credit simultaneously, has more than doubled to almost 26,000 a year.

But while the courses are free to students, they’re costly for the colleges that sponsor them, said Jessica Espinosa, who oversees the dual credit programs at the Minnesota State colleges and universities.

The system decided to raise its fees — from as low as $1,500 a course to $3,000 or more — out of financial necessity, she said: “What some of our campuses were charging was not covering their direct costs.” College faculty play a key role, she said, mentoring the high school teachers and ensuring that the courses are equivalent to those on campus.

Last year, the Higher Learning Commission, which accredits Minnesota’s colleges and universities, tightened the rules for college-in-the-schools programs. It announced that anyone who teaches courses for college credit must have graduate-level credentials, and it imposed a deadline for next September. When Minnesota State surveyed the 1,400 high-school teachers in its dual-credit programs, it found that only 24 percent met the new standards.

Last week, officials unveiled a plan that they hope will soften the impact of the change. They’re applying for a five-year waiver to give teachers until 2022 to earn graduate degrees. They’re also exploring other options, such as team-teaching and granting credit for real-world experience.

Still, Nathan argues that the Minnesota State system is taking a hard line that will force teachers — or their school districts — to waste millions on graduate school.

“If somebody has done a marvelous job of teaching biology or history or whatever for years,” he asks, “why not let her or him continue to do so?”