For tens of thousands of the nation's teachers, it is the start of an endless summer. In the past month, the Los Angeles Unified School District has sent pink slips to 693 employees. The Detroit school system has laid off 1,983 teachers, including Michigan’s 2007 teacher of the year. And Greensboro, N.C., has received national attention for firing or reassigning more than 500 teachers in a district serving just 71,000 students.