The preliminary findings of a new study suggest the worst teachers can be detected within their first two years on the job, according to a report by Education Week. The study, done by researchers at the Center on Education Policy and Workforce Competitiveness, looked at data from New York City elementary schools to determine how teachers improve over time. Although experts agree that most teachers show dramatic improvements within the first five years, the study found that the most effective and least effective teachers showed only slight changes over time.