No doubt we should blame TEH TEACHERS UNIONS! for this (boldface mine):

Nearly two-thirds of U.S. middle-school teachers work in schools where more than 30 percent of students are economically disadvantaged. This is by far the highest rate in the world, and more than triple the average TALIS rate. The next countries in line after the United States are Malaysia and Chile. Ignored by our current education policies are the facts that one in four American children lives below the poverty line and a growing number are homeless, without regular access to food or health care, and stressed by violence and drug abuse around them. Educators now spend a great deal of their time trying to help children and families in their care manage these issues, while they also seek to close skill gaps and promote learning.

Along with these challenges, U.S. teachers must cope with larger class sizes (27 versus the TALIS average of 24). They also spend many more hours than teachers in any other country directly instructing children each week (27 versus the TALIS average of 19). And they work more hours in total each week than their global counterparts (45 versus the TALIS average of 38), with much less time in their schedules for planning, collaboration, and professional development. This schedule — a leftover of factory-model school designs of the early 1900s — makes it harder for our teachers to find time to work with their colleagues on creating great curriculum and learning new methods, to mark papers, to work individually with students, and to reach out to parents.

As you might imagine, this affects teacher training (boldface mine):

Partly because of the lack of time to observe and work with one another, U.S. teachers receive much less feedback from peers, which research shows is the most useful for improving practice. They also receive less useful professional development than their global counterparts. One reason for this, according to our own Schools and Staffing Surveys, is that, during the NCLB era, more sustained learning opportunities reverted back to the one-shot, top-down, “drive-by” workshops that are least useful for improving practice.

Many education reformers come from or are influenced by business. As a result, they think there is a plentiful surplus of people just waiting to teach. There isn’t*, so we’re left with professional development as the primary tool to improve teaching (which, if you look at test scores doesn’t affect them all that much**). Despite all the education reform blather about teacher quality, they don’t seem to have any real solutions other than fire them and hope you can find adequate replacements. Doesn’t seem to do much for the students though.

*If you look at the NCES data, about one in six new college graduates has to go into teaching just to make up for the retirements (assuming no other people decide to become teachers).

**Where teachers do seem to have a large effect is on future life outcomes (e.g., graduation, staying out of jail). These, however, aren’t really correlated with subject matter test scores.