Utah is one of four states that have not faced litigation on the issue of school funding.
Those lawsuits have yielded mixed results, but the Alliance for a Better Utah sees victories in South Carolina, Washington and Kansas as setting optimistic precedents.
In those three cases, the states' supreme courts ruled that schools were underfunded and directed lawmakers to take action to adequately support education.
Utah spends the least per student of any state in the nation, a ranking typically attributed to larger-than-average families.
The state also ranks in the bottom half nationally for its funding effort, measured by the percentage of personal income that goes to support public education.
Matt Lyon, a consultant with the Alliance for a Better Utah, said changes to the state's tax code have decreased the burden on taxpayers while also eroding funding for schools.
"The state has made deliberate attempts through policy decisions to remove funding that would otherwise have gone to education," Lyon said.
The Utah Constitution directs the Legislature to "provide for the establishment and maintenance of the state's education systems."
Lyon said the lawsuit will question the definition of "maintenance," arguing that state leaders have done little to offer educational opportunities for students.
Fewer than half of Utah students are reaching grade-level benchmarks in math, science and English, according to the most recent year-end-test data.
And about one-fourth of graduating seniors are "college ready" based on benchmarks set for the ACT test, which is taken by all Utah high school students.
Those scores are even worse for Utah's minority students, who lag behind their white peers by one of the widest margins in the United States, according to data from the National Center for Education Statistics.
"If you look at educational results in Utah," Lyon said, "it's clear that we're not meeting those minimum standards."
House Speaker Greg Hughes, R-Draper, said the state would be in a strong position to defend itself against a lawsuit.
Last year, lawmakers approved a $75 million property tax increase that primarily benefits school districts with low property values.
And the state generally receives high equity marks for its use of a weighted pupil unit, a funding formula that equalizes state per-pupil spending.
"I think you'd be hard pressed to show the state of Utah's formula and structure for funding schools is inadequate or unconstitutional," Hughes said. "I would say it's probably a best practice in terms of making sure all children within your state are funded in the appropriate way."
Thomas said it likely would be months before the lawsuit is filed. He said Alliance for a Better Utah is reviewing potential law firms and determining appropriate plaintiffs.
"Once we have a law firm chosen," he said, "then we'll be able to draft the complaint."
Senate President Wayne Niederhauser, R-Sandy, said schools would benefit from more funding, but he questioned the claim that the current funding is inadequate.
Despite its low funding levels, Utah has continued to make gains on metrics like graduation rates.
"If we want to be the No. 1 state on education, we can't fund it adequately," he said. "We have to fund it more than adequately, and I hope the Legislature will address that."
With the Legislature in session and the potential of a yearslong court battle, Thomas acknowledged that the group's complaint could become moot if lawmakers take action.
But if they don't, he said, then Alliance for a Better Utah is committed to pressing the issue and winning in court.
"We'd be happy to not have to go through with it," Thomas said.
David Crandall, chairman of the state school board, said it's unclear whether the state is vulnerable to litigation on the subject of school funding.
He pointed to Washington, D.C., where per-student spending is among the highest in the nation, yet educational outcomes remain low.
"It begs the question, what is the correlation between the amount you're spending and the results?" he said.
Crandall said school districts and the state school board would find effective uses for new and increased funding.
But he added that he would be uncomfortable with the judicial branch setting or directing spending levels for public education.
"You also have to weigh the impact that additional taxes are going to have on the economy and, indirectly, on residents," he said. "That's still something that's probably best handled through the legislative process."
Utah Gov. Gary Herbert said the state has unique challenges, with high birth rates and large families spreading resources thin. But Utah students continue to compete nationally despite low funding levels.
"We're getting a good return on our dollar here," he said. "We've got great teachers here in Utah, great principals, superintendents, school board members, parents and students."
Earlier this week, Utah's business community called for a $500 million tax increase to be placed on the November ballot.
The vote would be nonbinding, but organizers say it could provide lawmakers with the political cover to increase funding for schools during next year's legislative session.
But Josh Kanter, founder of the Alliance for a Better Utah, said a public vote would only delay what opinion polls have consistently shown to be supported by taxpayers.
The governor and lawmakers need to take action, he said, or be required to by court order.
"It doesn't take a ballot initiative," Kanter said. "We know where the public stands. The public wants more education funding."
Tribune reporter Robert Gehrke contributed to this report