This brief focuses on what we know about how the Pre-K CLASS relates to children’s outcomes in general, and whether its relationships with outcomes differs for key subgroups of children. By summarizing findings of the most recent studies published in the field, we can learn more about how and when quality measures relate to children’s outcomes, the reasons why the strength of those relationships might be modest, and if there is the need to expand existing measures of quality. We conclude with some implications these findings have for practice and future research. (author abstract)