Before districts go replacing veteran teachers with 5-week wonders from TFA, they should consider this. 

Research has been consistent in finding positive correlations between years of teaching experience and higher student achievement. Teachers with more than five years in the classroom seem to be the most effective. Conversely, inexperience is shown to have a strong negative effect on student performance. 

• Experienced teachers produce higher student test scores. A comprehensive analysis by Greenwald, Hedges, and Laine (1996) examined data from 60 studies and found a positive relationship between years of teacher experience and student test scores. Similarly, the UTD Texas Schools Project data showed that students of experienced teachers attained significantly higher levels of achievement than did students of new teachers (those with one to three years of experience) (Rivkin, Hanushek, and Kain 2005).

• Schools with more inexperienced teachers have higher drop-out rates. In a related finding, an analysis of math achievement and dropout rates in a sample of California high schools (Fetler 2001) found that schools whose dropout rates were in the highest 10 percent had 50 percent more new teachers than did schools in the lowest 10 percent. -- The Center For Public Education