necessary measures (id.) and remitted to Supreme Court for further proceedings in accordance with our opinion (100 NY2d at 932). Within a matter of weeks, Governor Pataki issued an executive order creating the New York State Commission on Education{**8 NY3d at 22} Reform, charged with recommending, to the Executive and the Legislature, education financing and other reforms that would ensure that all children in New York State have an opportunity to obtain a sound basic education. The Commission, chaired by Frank G. Zarb, published its final report on March 29, 2004. The Zarb Commission retained Standard and Poor's (S & P) School Evaluation Services to calculate the additional spending required to provide a sound basic education, directing S & P to use a "Successful Schools" model that studies the expenditures of school districts with a proven track record of high student performance. The method had been used by the New York State Board of Regents in its Proposal on State Aid to School Districts for 2004-05. The Zarb Commission developed three alternative criteria for identifying successful school districts. One option was based on New York's 2007-2008 performance [*4]standard set in accordance with the federal No Child Left Behind Act of 2001. Another was similar to the first but substituted the 2006-2007 performance standard. The third criterion was the same approach to identifying successful schools that the Board of Regents had used; it picked out school districts281 of 699in which at least 80% of the students performed at or above a proficient level, over a three-year period, in seven tests required by the Board of Regents: two fourth-grade examinations and five examinations required for high school graduation.[FN2] Reasoning that not all successful schools operate in a manner that is economical, the Zarb Commission instructed S & P to apply a cost-effectiveness filter: once successful school districts were identified by the methods just described, they were to be ranked according to expenditures and those in the lower-spending half were to be used to create an average. The Board of Regents had noted the necessity for applying such an efficiency filter, because "districts that perform at high levels often enjoy a very substantial wealth base, and therefore also spend at very high per pupil[ ] levels" (Regents Proposal on State Aid to School Districts for 2004-05, at 48, available on the Internet at{**8 NY3d at 23} , cached at ). Drawing on an extensive review of pertinent research literature, S & P applied three weightings to the resulting base expenditures, in order to take into account the greater spending required for students with special needs. The coefficients by which the base expenditures were multiplied were 2.1 for students with disabilities, 1.35 for economically disadvantaged students, and 1.2 for students with limited English proficiency. S & P cautioned that it was not in a position to recommend explicitly the set of weightings it applied. Adjustments were also made to account for the local purchasing power of the dollar, using two, alternative cost indices, the New York Regional Cost Index (NY RCI), provided by the New York