Because this type of assessment is like the development of expertise in the real—or authentic—world by real workers. How often do sculptors just sit down and knock off a new piece? Which authors don't write multiple drafts? How many scientists make a big break with the first experiment? In order for their students to develop expertise, teachers need a lot of professional development that is embedded in the content they teach; around the kinds of tests they want students to engage in; with colleagues trying strategies and debriefing them together, fine-tuning their plans, developing what I think of as a two-way pedagogy in which teachers learn to listen to students and look at student work, so that they get information about the learning process,as well as directly instruct students and provide information. That reciprocal kind of pedagogy is part of what gets refined in professional development with colleagues when teachers continually bring student work to the table and problem solve the teaching and learning process with colleagues.