The equalization formula used by 81 percent of Illinois school districts to compute their state aid was designed to meet the requirement of fiscal neutrality established in Serrano v. Priest. However, the inclusion of the operating tax rate in the resource equalizer formula tends to help income-rich school districts more than income-poor districts. This study investigated the effect of various income-weighted operating tax rates on the distribution of state aid. Three approaches--per capita weighting, grouped weighting of median family income, and individual weighting of median family income--were tried on all districts, except secondary, in the state. The variables examined were the type of community (central city, suburb, independent city, or rural area), effect on district expenditure variation, and effect on fiscal neutrality. It can be concluded that the per capita method would be the best weighting to be applied to the operating tax rate. Per capita weighting is the best in measure of fiscal neutrality and offers other advantages--it does not penalize districts with above average income and it provides more opportunity for income-poor districts to fully participate in the state aid system. (Author/IRT)