DENVER — Colorado’s highest court on Monday struck down a voucher program that allowed parents in a conservative suburban school district to use taxpayer dollars to send their children to private schools.

The split decision to throw out the voucher program in Douglas County, Colorado’s third-largest school district, was a blow to conservative education advocates and those who want to redefine public education to funnel tax dollars directly to families who then choose the type of schooling they want for their children.

The state’s Supreme Court ruled against the district’s voucher program, which was passed in 2011, saying it violated a plank of the State Constitution that explicitly prevents public money from going to schools “controlled by any church or sectarian denomination whatsoever.”

“This stark constitutional provision makes one thing clear,” Colorado’s chief justice, Nancy E. Rice, wrote in the court’s opinion. “A school district may not aid religious schools.”