As summarized by Jonathan Kantrowitz, " The new report, California’s Positive Outliers: Districts Beating the Odds, finds that the proportion of teachers holding substandard credentials—such as emergency permits, waivers and intern credentials—is significantly and negatively associated with student achievement for all students." (44 page PDF) This stands in contrast to the other report I read today emphasizing the role of family income in education outcomes. But for this report we have to read carefully and sometimes between the lines. As the authors write, "We find that, aside from socioeconomic status, a major predictor of student achievement is the preparedness of teachers." So there's isn't really a contradiction between the two reports, just a (potentially misleading) difference in emphasis.