As of April 2018, several of the largest U.S. mutual fund firms have been imposed to disclose a measure of fund manager activeness to retail investors. We evaluate the effectiveness of this intervention. We find that, even for those funds with a large overlap of holdings with the benchmark, no measurable effort to increase management activeness can be observed subsequent to the imposed disclosure. By contrast, investors strongly respond to the intervention. However, an analysis of investor reaction suggests that they do not rationally trade on the newly available information. We discuss our results and propose potential disclosure improvements.