The trial in the lawsuit from teacher unions and local school boards seeking to shutdown a statewide voucher program began Wednesday.
A state judge heard more than eight hours of complex testimony in 19th District Court.
The state Department of Education estimates it will cost about $25 million to send more than 4,900 students to private schools with vouchers this year.
The two unions and 43 school boards that filed suit over the voucher program claim that that money is being used illegally through the public school funding formula known as the MFP.
In its defense, the state called LSU Economist Jim Richardson to argue that the cost of the voucher program does not constitute a loss to school districts. But in cross examination, Richardson said he had no doubt that when a child leaves for private school with a voucher the local district loses dollars.
At the conclusion of the day, Judge Tim Kelley framed the issue.
"If I determine that through the MFP mechanism a private enterprise cannot be funded, the plaintiffs are right?" Kelley asked Richardson.
"Their argument is correct from a legal perspective," Richardson said.
The first day of testimony also included a crash course in the legislative process, which the plaintiffs claim was violated when the MFP was passed. House Clerk Butch Speer explained his advice to House Speaker Chuck Kleckley that the state constitution allowed the funding formula to pass with 51 votes rather than a 53-vote majority of House membership.
Lawyers for both sides expect testimony to wrap up today. Judge Kelley says he expects to rule by the end of this week.