He has an excellent review essay in the New Yorker. The main point, of course, is that (a) a fairly big part of the American education system -- at school and university levels -- works, and works well, and (b) it is important to identify specific problems to be solved through specific remedial actions -- big bang "reforms" could be lethal!
Let me just say that I find Lemann's thesis so appealing for its sheer reasonableness.
Here's an excerpt from the concluding section of he article [with bold emphasis added by me]:
There have been attempts in the past to make the [vast] system [with all its overlaps and competitive excess] more rational and less redundant, and to shrink the portion of it that undertakes scholarly research, but they have not met with much success, and not just because of bureaucratic resistance by the interested parties. Large-scale, decentralized democratic societies are not very adept at generating neat, rational solutions to messy situations. The story line on education, at this ill-tempered moment in American life, expresses what might be called the Noah’s Ark view of life: a vast territory looks so impossibly corrupted that it must be washed away, so that we can begin its activities anew, on finer, higher, firmer principles. One should treat any perception that something so large is so completely awry with suspicion, and consider that it might not be true—especially before acting on it.
We have a lot of recent experience with breaking apart large, old, unlovely systems in the confidence of gaining great benefits at low cost. We deregulated the banking system. We tried to remake Iraq. In education, we would do well to appreciate what our country has built, and to try to fix what is undeniably wrong without declaring the entire system to be broken. We have a moral obligation to be precise about what the problems in American education are—like subpar schools for poor and minority children—and to resist heroic ideas about what would solve them, if those ideas don’t demonstrably do that.