A California court case-begun in 1968 and settled in the mid-1970s-that challenged the inequities created by the U.S. tradition of using property taxes as the principal source of revenue for public schools, saying the wide discrepancies in school funding because of differences in district wealth represented a denial of equal opportunity. In response, legislators passed Senate Bill 90 in 1972, creating the revenue limit system that put a ceiling on the amount of general-purpose money each district could receive.