In this final chapter of UNDERSTANDING BY DESIGN, the authors explicitly address the three biggest objections they have faced with the UbD approach: namely, the need to "teach to the test", the excess of content that must be taught, and the lack of teacher time to implement these plans.
They answer all of these objections ably. While they are realistic about the pressures that teachers are under to perform, they are also brutally honest about the present state of affairs: they point out, for instance, that the schools that perform the best on standardized tests aren't the ones that spend endless hours training students to take tests. They also address one of the concerns that I had about the UbD approach: namely, schools that implement it do see a rise in test scores among their students. It is possible to teach for understanding and still reap a "fringe benefit" of improved performance in standardized assessments.
One part of this chapter that I found interesting was the reference to a collaborative curriculum-planning community called UbD Exchange. Apparently there are teachers all over the country who are using UbD and making their lesson and unit plans available over a shared website. I'll need to find out how we can access this service, because it would be a huge help to me in my ongoing lesson planning -- especially when I get ready to teach physics in the spring semester.