This is really the only significant part of the equation. The system is basically designed to fail. You pass a tax levy for X mills, which brings in X amount of money for the school system, and never a dollar more. Property values go up, but property taxes do not. The budget therefore shrinks every year due to inflation, and every 10-15 years the situation gets so dire that the district has to put a ballot issue up for a tax "increase" to get funding back up to the levels of 10-15 years ago.
In most areas of the Midwest, this poor voter understanding of how schools are funded has resulted in a steady decline in school expenditures, even as actual costs of education have outpaced inflation.