At least sixteen US states have taken steps toward holding teacher preparation programs (TPPs) accountable for teacher value-added to student test scores. Yet it is unclear whether teacher quality differences between TPPs are large enough to make an accountability system worthwhile. Several statistical practices can make differences between TPPs appear larger and more significant than they are. We reanalyze TPP evaluations from 6 states--New York, Louisiana, Missouri, Washington, Texas, and Florida--using appropriate methods implemented by our new "caterpillar" command for Stata. Our results show that teacher quality differences between most TPPs are negligible--0.01-0.03 standard deviations in student test scores--even in states where larger differences were reported previously. While ranking all a state's TPPs may not be possible or desirable, in some states and subjects we can find a single TPP whose teachers stand out as significantly above or below average. Such exceptional TPPs may reward further study. [This research was supported by a grant from the Policy Research Institute at the University of Texas, Austin.]