[originaltext]　　The old-fashioned practice of rating instructors by watching th

　　The old-fashioned practice of rating instructors by watching them teach is tricky, labor-intensive, potentially costly and subjective—(19) but perhaps the best way to help them improve, according to a study released Friday. The findings highlight the importance of teacher observations, but also pinpoint why they frequently don’t work. The old way—observing a teacher once a year, or once every five years in some cases—is insufficient. (20) And the observers, typically the school principal, frequently don’t know what to look for anyway. But that doesn’t mean teacher observations should be tossed aside. The best way to evaluate teachers, while also helping them improve, is to introduce an updated teacher observation system, the report found. The traditional approach in the school’s system of the Memphis, Tennessee, has long included teacher observations—once every five years. Principals would receive some initial training, but no one certified their evaluation skills or monitored their success. Of these, about 98% of teachers were rated as effective, while they received little feedback that would help them improve and little opportunity to share proven techniques with colleagues. Under a new system, teachers are observed four to six times annually by more than one person. Evaluators must pass a certification program that involves analyzing sample lessons to see if their skills match those of the committee that includes teachers, principals and other administrators. (21) Teachers get detailed feedback on observations within seven days. The new strategy isn’t perfect, but far surpasses traditional practices, which frequently offer little evaluation of any kind. Getting classroom observation right is tough work but a critical component.
　　19. What does the study say about the old-fashioned way of rating instructors?
　　20. Why do traditional teacher observations fail to work frequently?
　　21. How does the new system of teacher observations work?