The long slog through another legal challenge to Texas' system of public school finance has begun. Opening arguments were held Monday in the trial of six lawsuits combined into one case before state District Judge John Dietz in Austin.The trial is expected to last through January, and the case undoubtedly will go to the Texas Supreme Court. Lightning-fast action there could mean a final judgment by next summer.But don't get your hopes up. The last such case went more than four years from start to finish, including two trips to the Supreme Court.Even that's not the final bar to clear. After a Supreme Court ruling will come legislative debate on a court-required solution -- unless the state successfully defends the current funding mechanism, which hasn't happened in 28 years of previous cases.Most of the legal ground has been plowed before -- but not all. Still, the five previous rounds of school finance lawsuits brought fundamental change to the way Texas pays for public education, with huge impact on schools and students.The new ground this time, brought into play by a group of plaintiffs from an organization led by former state Rep. Kent Grusendorf of Arlington, provides an intriguing element. The complaint from Texans for Real Efficiency and Equity in Education is that the state doesn't know what's the right amount to spend on its schools, and besides that public schools can only perform at their highest level if they lose their lock on the primary and secondary education market.Four groups of school districts brought suits that began the current case. Together, those complainants include more than half of the districts in the state, which enroll three-fourths of Texas' 4.9 million public school students.Each of those groups has specific arguments against the school finance system, but they unite in saying that the system violates the state constitution.That was the Supreme Court's ruling in the last major school finance case in late 2005. Schools draw most of their local funding from property taxes, and their tax rates are limited under state law. The state is constitutionally blocked from levying a property tax.The state also sets education standards. The Supreme Court has said when districts must exhaust their available property tax revenue to meet state standards that means the districts have lost "meaningful discretion" over their spending. In turn, that means the state has unconstitutional control over their property tax.An association representing charter schools also filed suit, with the additional argument that the state must lift its limit on the number of charters it will grant.Finally, there's Grusendorf's group, which has been joined by the Texas Association of Business. They want the state to do more to determine how much is the right amount to spend per student. That "adequacy" argument has not proven very effective in previous Texas cases or those in some other states. It's an almost-impossible number to tie down.But the other part of the group's argument, that the public education monopoly is inefficient and should be broken up, is unique and worth watching. It's basically an argument for private school vouchers, which is a fight that Grusendorf led when he was in the Legislature.All of the plaintiff groups will use the coming months of expert testimony and stacks of evidence to impress Dietz and introduce every element of their case in preparation for argument before the Supreme Court.Progress will be snail-slow, but little that happens in Texas has more impact than its schools.