Tennessee officials never expected long lines for a new program that would allow parents of students with disabilities to spend up to $6,000 a year in public funds on private schooling.

Sure enough, the program, now in its third month, has enrolled just 35 students, out of 20,000 eligible — though school choice advocates say they are heartened by the program’s potential to grow.

Tennessee lawmakers passed the Individualized Education Act in 2015 to give students with certain disabilities public money for private services such as homeschooling, private school tuition, and tutoring. The catch: Students must leave their public school and waive their rights under the federal Individuals with Disabilities Education Act, which mandates that all students receive a “free and appropriate” public education. That type of program has been lauded by U.S. Secretary of Education Betsy DeVos, who has said they “empower” parents to make the best decisions for their children.

But in its first year, only 130 families applied for Tennessee’s program. Just a third of those applications actually were approved, and even fewer ultimately decided to participate.

Many forces conspired to keep the number low. For one, the program started in the middle of the school year, a time when parents are unlikely to want to shake up their child’s education.

Plus, only eight private schools got the state’s approval to accept students using vouchers. Many private schools aren’t set up to deal with different disabilities.

Often, private schools charge far more than $6,000, with the tuition at Memphis-area private schools topping out at more than $20,000 a year. Public schools on average spend about $16,000 per special education student.

“Families are going to be very wary about leaving a system that’s legally and by capacity going to be able to do pretty well by their kids, than for a wish and a prayer from private schools that don’t have that track record,” said Jeffrey Henig, a political scientist at Columbia University who has studied private school choice.

Tennessee’s program for students with disabilities could grow significantly if a bill up for vote in the Senate Education Committee this week becomes law. The bill would allow families who have never sent their children to public school to take advantage of the program, too. In other states, including Indiana, the number of students using vouchers swelled when the requirement to first enroll in a public school was lifted.

The Senate panel also is set to consider multiple proposals for school choice programs for students without disabilities, including vouchers. Unlike traditional voucher programs, where money goes directly to a private school, the state pays participating parents in installments on a debit card.

Lindsay Boyd, policy director for the Beacon Center, a free-market think tank that advocated for the program, said that enrollment isn’t the only measure of success.

“We view success as parents being able to find a unique and customized education path that suits their child’s needs,” she said. “If that’s five parents, that’s an improvement.”