Voters are often uninformed about the political candidates they choose between. Governments, media outlets, and civic organizations devote substantial resources to correcting these knowledge deficits by creating tools to provide candidate information to voters. Despite the widespread production of these aids, it remains unclear who they reach. We collect validated measures of online voter guide use for more than 40,000 newspaper readers during a state primary election. We show this newspaper-produced voter guide was primarily used by individuals with high levels of political interest and knowledge, a finding in contrast to earlier hypotheses that providing guides directly to voters online would reduce disparities in use based on political interest. A field experiment promoting the voter guide failed to diminish these consumption gaps. These results show that the same content preferences that contribute to an unequal distribution of political knowledge also impede the effectiveness of subsequent efforts to close knowledge gaps.