The South Dakota Supreme Court on Thursday upheld the constitutionality of the state's system for funding school districts, rejecting the schools' arguments that the current arrangement does not provide enough money to assure students of an adequate education.

In a unanimous ruling, the high court said a lawsuit supported by about two-thirds of the state's school districts raises serious questions about the funding system and shows that some districts struggle to provide adequate facilities and qualified teachers.

"Even so, reasonable doubt exists that the statutory funding mechanisms or level of funding are unconstitutional," Justice Judith Meierhenry wrote for the court.

The 41-page main decision upholds a ruling by Circuit Judge Lori Wilbur of Pierre, who ruled in 2009 that the school funding system is constitutional because it provides students with an adequate education that prepares them for life after high school. Wilbur has since been appointed to the Supreme Court, but did not take part in Thursday's ruling.