Substantial evidence exists that members of the US Congress vary in their lawmaking effectiveness. Less known, however, is whether constituents are sufficiently informed and inclined to hold their representatives accountable, based on their effectiveness. We conduct two separate survey experiments, informing some constituents about lawmakers' effectiveness and comparing their responses to those with the baseline level of information. We find that voters demonstrate little knowledge of their elected officials' lawmaking effectiveness. When presented with objective and credible information about lawmaking effectiveness, however, respondents express greater approval of more effective lawmakers. Effects are strongest among ideological moderates, but are even pronounced among partisans, who approve of effective representatives of the opposing party, and disapprove of ineffective representatives from their own party.