From the article:
Consider TFA’s two original missions: first to help understaffed school districts fill teaching positions with talented, energized college graduates, and second to create a broader education advocacy and awareness movement. On both counts, TFA has had an impact, but ironically as TFA continues to grow, in many ways its impact is fading.
No longer are TFA corps members only filling spots that would otherwise go to long-term subs. In some districts TFAers are replacing veteran teachers who have been let go. Other districts, like the one I used to teach in, appear to cycle through corps members every two years, with high turnover among TFA teachers who are in turn replaced by a fresh slate of bushy-tailed, ill-trained corps members.