I myself am a lawyer, but I come from a family of teachers. I can't stand TFA, and I think it causes more harm than good. Let me tell you why:
1) Practical Issues: If TFA were used purely as a supliment to actual hired teachers I could see some benefit to it as it would decrease class size and allow more veteran teachers to tackle more difficult classes. However TFA is too often used by schools as an "instead of" option not an "in addition to" proposition. Schools will too often opt to not hire new staff knowing that they are getting TFA participants and they can keep their class sizes under State and Federally mandated maximums. These positions would be better filled with actual teachers.
2) Perception Issues: TFA fosters the perception that teaching isn't a profession, but it simply a job. It undermines the great skill and training required to become a successful teacher. Can you imagine a program called "Lawyer for America" where young college grads could practice law at the Public Defenders Office for two years? Or "Doctor for America" where college grads with minimal training could preform surgery in inner city hospitals? These programs seem ridiculous and illustrate how we view lawyers and doctors as more professional than teachers.
3) Academic Issues: TFA undercuts the importance of an eduucation in education. The notion that enrgy + knowledge of a subject = good teaching is absurd. Good teachers are trained is child or adolescent psychollogy. They understand the complex methodology of teaching and have studied divergent views of pedagogy. They have spent 6 months to a year in practicum leaning from a master teacher and learning their craft.
TFA ignores all these issus and place underqualified, undertrained individuals in classrooms that often need the most training and skill.
If these college grads truly wants to make a difference they might want to think about getting an actual teaching credential.