Principals are under increasing pressure to raise student test scores. The vast majority of their teachers are committed and competent, principals say, but an unknown number stifle learning. Given the extreme difficulty of terminating a tenured teacher, what's a principal to do once she has tried without success to help the teacher improve? According to Dr. Robert Mendro, the assistant superintendent for research and evaluation at Dallas Public Schools who has used value-added analysis to analyze the effectiveness of teachers in the district, "To date, there is little evidence that principals turn around the performance of teachers. Rather, effective principals do not tolerate having ineffective teachers on their staffs." In an article by reporter Scott Parks in The Dallas Morning News, principals candidly describe the tactics they use to get rid of bad teachers, which include becoming a constant presence in the teacher's classroom, giving a teacher hallway duty, putting a teacher on marginal committees, denying a teacher a permanent classroom, or giving a teacher a new grade or classroom assignment in which he or she is expected to be unhappy. A teachers union representative counters with the other side of the coin-what he calls horror stories of teachers suffering at the hands of vindictive and capricious principals. For details see "Bad teachers get push toward door," by Scott Parks, The Dallas Morning News, February 3, 2002.