I haven't had time to much more than skim the conclusion, but the Washington State Supreme Court has ruled against the state in McCleary v. State:

The State has failed to meet its duty under article IX, section 1 by consistently providing school districts with a level of resources that falls short of the actual costs of the basic education program. The legislature recently enacted sweeping reforms to remedy the deficiencies in the funding system, and it is currently making progress toward phasing in those reforms. We defer to the legislature's chosen means of discharging its article IX, section 1 duty, but the judiciary will retain jurisdiction over the case to help ensure progress in the State's plan to fully implement education reforms by 2018.

The court has upheld the lower court ruling that the state has failed to adequately fund K-12 education, but did not order remedies. Instead, it will defer to the legislature through 2018, while retaining jurisdiction. In other words, the opinion is both dramatic and a cop-out at the same time.

Politically, I'm not sure what this means for the coming legislative session. Probably very little.