I would say that my time with Teach for America resembles what I imagine a Peace Corps experience to be like.

I went in with the best intentions, completed my life entirely to my students for two years, made huge strides with the students in my classroom, built some meaningful relationships with my students, and then I left. Since leaving, I've continued to incorporate educational initiatives into my daily life and work on education/technology projects at my current company. From my friends who have done the Peace Corps, they say that their experience is pretty similar - immersing oneself into a world, doing the best you can to understand the needs of the community and the cultural implications of the work you are carrying out, and leaving after two years. After one leaves these roles, you don't know if the ground work you carried out will be continued; whether in the trajectory of a student's reading abilities or in a well being built in a village. Are either going to be maintained after you left? Maybe, maybe not. But is it not better for that well/that student to have been invested in in the first place?

Here is where the question of "improving the quality of education" comes in. Is it better for people to devote this time to education than to say...become a consultant or investment banker? If I had chosen a more traditional path after college, my life and the lives of the students that I would have been different. I can't argue that if I hadn't done Teach for America, the lives of my students would have been better. Another traditionally certified teacher certainly could've done a better job. But do I think my student's lives were worse off because of my time in the classroom? I really, really hope not. From the relationships I've maintained with my students, I know that at least a handful were really changed by my time with them, and I would count that as a win. So I think that my student's lives were benefited by my time, but that is only one measure of their education.

I think it really boils down to the intent of your question - how are you measuring quality of education?
-By student test scores
-By student engagement in class
-By how long a teacher stays in the profession
-By the amount of training a teacher has
-By the time a teacher devotes to their students
-By the innovation that a teacher brings to the classroom

To speak to Ben's point that "TFA does nothing to address the problems with teachers unions, testing, standards, bureaucracy, teacher salaries, and funding that are actually essential to fixing public education", I'm not sure if I see that as the goal of Teach for America while a Corps member is in the classroom. Rather, I see that as the role of TFA alumnus who go off into their respective fields. Many Corps members stay in education, but a lot go into business, law, etc. I would argue that by having people in these fields with a passion for education, TFA will have a long-term effect on the types of issues that are at the root of our educational system. When college students who just as easily could've become a consultant become a lawyer championing for educational rights, or an engineer who can build a tech start up that increases student engagement in the classroom, the long term ripple effect of TFA can be unlimited.