$10 million spent annually by district for classroom subs... Driven by parental concerns about teacher absenteeism, the Chicago Public Schools for the first time will start scrutinizing schools with high numbers of teachers taking sick days. On any given school day in Chicago, an average of 1,500 teachers, about 6 percent of the teaching staff, call in sick or take a personal day, according to a Tribune analysis of teacher payroll records. The absentee rate is highest on Fridays, when an average of 1,800 teachers don't show... For each of the last six school years, Chicago teachers missed an average...