SPRINGFIELD, Ill. — Patti Serpa is a single mother of five who relies on a state-sponsored tax credit to send her youngest, 12-year-old Santos, to St. Pius V School, a Catholic grade school in Chicago’s Pilsen neighborhood that she feels provides him with a better education than his former public school. “Being at St. Pius, it’s a family,” Serpa said in Springfield last week, where she and ...