The quality of the teacher workforce is a subject of perennial concern in many developed countries. In the United States, through the "No Child Left Behind" (NCLB) Act, the federal government has a mandate for reform of teacher education that is unprecedented in its scale. Essentially the Act demands that every teacher of core academic subjects must be deemed to be highly qualified in every subject they teach by the end of the 2005-2006 academic year. This paper considers the impact that NCLB's teacher quality mandate is having in US schools. By drawing upon school-level data for the state of California, we examine the progress that this state is making towards meeting NCLB's mandate and also the role that teacher quality can play as a determinant of school success. The findings suggest that overall California has a well-qualified and highly experienced teacher workforce which is relatively equitably distributed among the states' institutions. On the other hand, the distribution of California's students appears to be less fair, with students from poorer homes and certain ethnic backgrounds being disproportionately represented in the state's least wealthy and least successful schools. In addition, the finding that it is student background factors rather than teacher quality characteristics that are the key determinants of school success, also brings into question the extent to which requiring teachers to improve their subject content skills will really help close the achievement gaps in California's schools.