The union leader for 19,000 public school teachers in Philadelphia predicted a strike, while teachers continued to negotiate in Chicago. Strikes continued in seven smaller school districts in Michigan, Pennsylvania and Illinois. In Philadelphia, the teachers' contract was set to expire at 12:01 a.m. today. The district demands a longer work day for teachers and control over how they use a 45-minute preparation period. Chicago's teachers want pay increases guaranteed in the second year, while school officials want an escape clause to avoid paying raises if money is tight.