OLYMPIA — The Washington Supreme Court on Thursday ordered the state pay $100,000 a day in sanctions, starting immediately, for its lack of progress toward fully paying the cost of basic education.

The ruling was the latest development in a long-running impasse between lawmakers and justices, who in 2012 ruled that the state is failing to meet its constitutional duty to pay for the cost of basic education for its 1 million schoolchildren.

Thomas Ahearne, an attorney for the plaintiffs, said that the court’s action “is long overdue.”

“The state has known for many, many years that it’s violating the constitutional rights of our public school kids,” Ahearne said. “And the state has been told by the court in rulings in this case to fix it, and the state has just been dillydallying along.”

Most states have faced lawsuits over the way they pay for education, but few have seen that conflict result in a contempt order like the one issued in Washington, one expert said.

The lawsuit against the state was brought by a coalition of school districts, parents, teachers and education groups — known as the McCleary case for the family named in the suit.

In its original ruling, and repeated in later follow-up rulings, the justices have told the Legislature to find a way to pay for the reforms and programs they had already adopted, including all-day kindergarten, smaller class sizes, student transportation and classroom supplies, and to fix the state’s overreliance on local tax levies to pay for education. Relying heavily on local tax levies leads to big disparities in funding between school districts, experts say.

In its ruling Thursday, the court encouraged Gov. Jay Inslee to call a special legislative session to address the issue, saying that if the Legislature complies with the court’s previous rulings for the state to deliver a plan to fully fund education, the penalties accrued during a special session would be refunded.

In a written statement, Inslee didn’t indicate if he would call a special session, saying that he will talk with the attorney general, legislative leaders and other to analyze the order.

“The court today made it clear that bolder and more aggressive action is needed to support Washington’s students and their teachers,” Inslee wrote. “The detailed plan the court demands in order to fulfill our constitutional obligation will be more complex and expensive than the significant steps we’ve already taken.”

Earlier this year, the Legislature approved what it called a $1.3 billion down payment toward fully paying the cost of basic education, an amount critics said fell billions of dollars short.

Last month, the attorney general’s office argued in a filing to the court that it should dissolve its current contempt order against the state. Senior Assistant Attorney General David Stolier wrote about the various ways the Legislature has fulfilled the high court’s 2012 McCleary decision on the funding, and he said the state is on schedule to meet all the requirements of the court.

While the court acknowledged that progress was made by lawmakers during this year’s triple overtime legislative session, it said the state failed to provide a plan for full compliance by the 2018 deadline.

“The State has not shown how it will achieve full funding of all elements of basic education by 2018,” said the order, signed by all nine of the court’s justices. “The State urges the court to hold off on imposing sanctions, to wait and see if the State achieves full compliance by the 2018 deadline. But time is simply too short for the court to be assured that, without the impetus of sanctions, the State will timely meet its constitutional obligations.”

The court wrote that monetary sanctions are an appropriate act by the court, and they are “an important part of securing the promise that a court order embodies: the promise that a constitutional violation will not go unremedied.”

The order calls for the sanctions to go to a special account “for the benefit of basic education.”

Only a few other state governments have faced similar sanctions in recent decades. In 1976, New Jersey’s Supreme Court ordered public schools shut down for eight days over the summer after lawmakers failed to put more money into education. That crisis resulted in the adoption of a state income tax.

David Sciarra, executive director of the Newark, New Jersey-based Education Law Center, which provides assistance to lawyers across the country on education financing cases, said that the New Jersey case was the closest comparable situation to the sanctions issued Thursday in Washington state. He noted a federal ruling involving Arizona over bilingual education that resulted in a fine to the state, but was later overturned by the 9th Circuit Court of Appeals.

He called the Washington court’s actions “extremely significant.”

“This is really a court that is obviously frustrated and fed up with ongoing noncompliance with its orders, consistently, over quite a long period,” he said. “There’s no other state court ruling in this area in a case involving inadequate school funding that has done this.”