Klein's point that the new tools of social networking are limited to "islands" within large district that are "Balkanized" is well taken. As to why this is the case, however, he suggests that a significant reason for this is, perhaps, money. My own research of this, based on the annual surveys of the California Department of Education, do not support this conclusion, however. Some schools, even with modern computers and Internet access, are opting not to allow their students to utilize available social networking tools (Mira Mesa High School, for instance). Since creating blog and wiki accounts are essentially free, the cost of doing so cannot be the reason for this.
Interestingly, Klein goes on and makes exactly this point. He describes how it is possible to create a vibrant social networking community at a K-12 school that is essentially cost free (assuming you already have a good IT guy at the district like Klein). He describes the various open source systems and software that can be used and made safe and secure for a school district's use. And I visited the school district site Klein is responsible for and it is certainly very good and worthy of emulation. Yet I also noticed that even as good as his site is, many of the teachers at his district are still not taking advantage of it. This suggests that the other problem then may simply be that too many teachers are either not literate in the use of the Web 2.0 world, or that there is a prevalence of luddism---an unwillingness to move along at the pace that technology can allow us.