C is for cookie, that's good enough for me. (Photo by Sarah L. Voisin/The Washington Post via Getty Images)

When we discuss the cost of school choicecharters, vouchers, and even homeschoolingwe usually focus on the economic impact, the loss of local control, or the policy impact on educational institutions. But on the classroom level, there is another real impact.

Robert Pondiscio touches on it in his new book about Success Academy charters schools, How The Other Half Learns:

The most common objection to charter schools and publicly financed charter school initiatives is that schools of choice siphon resources away from traditional public schools. One such resource is engaged and invested parents.

And, one might add, engaged and invested students. Every classroom culture is shaped not just by teachers and building administration, but by the students in the classroom. Students can have a huge effect on the tone of the classroomis there a steady pressure to achieve, or is acting smart just not cool? Particularly in high school, students learn about peer effects, about how to lead and how to elevate leaders. Strong students can raise a classs achievement level in ways that a teacher can not.

Most of us have stories. I learned to play trombone in high school in large part from trying to keep pace with the upperclassman who was my section leader. For four years, everyone in my core classes chased the two most intelligent, hardworking women in our grade. As a high school teacher, I saw the same effect over and over again. I could lay out expectations and standards and rubrics, but it is students (and sometimes by extension, their parents) who will answer the question, How seriously should we take any of this? That leadership will come from the strong students in the room. There are few things as exhilarating as teaching a class led by a core group of students whose attitude is, You just teach as fast and far as you can, because we want to see it all, and we will keep pace with you every step of the way, and so will the rest of these students. Right?

But what if those leaders arent there? Ive taught those classes, too. You make your best pitch and the students look around and conclude that nobody else is working all that hard, so theyll just take it easy, too. (Mr. Greene, Im not an over-achiever or an under-achiever, a student once told me. Im an even-achiever.) It is a huge challenge to light a fire under a room full of Cookie Monster students.

When stronger, more committed students leave a school, they leave that school with a bit less student leadership, a bit less positive peer effect. Their choice costs their former school something in the school culture and environment. That becomes more troubling when the strong student leaves for a school that doesnt offer any real benefits above and beyond the original public school.

The policy implications of peer effects are many. Can we even hope to measure these peer effects in any meaningful way, or will researchers just resort to using standardized test scores? If we can identify them, should we attempt to distribute good students evenly across the system? And how wildly inappropriate is it to treat students as a school resource rather than individuals working on educational goals of their own?

This is a tension thats almost impossible to resolve. It is hard to argue that a strong students family should keep her in the public school to serve a greater good, yet it seems clear that should she go to a charter, a private school, even a magnet or home school, there is a cost to the students who stay. Its a personal choice, but it has more than personal consequences, and they are hard to discuss in an age in which we have lost the language of civic obligation. But at a minimum, we should acknowledge that there is a cost here, and somebodyeither the school or the student or, in the case of students who choose a school no better than their old one, bothis going to pay it.

More here:
The Other Cost Of School Choice - Forbes