Now, a new study has failed to replicate Hart and Risley's findings, further complicating the legacy of this body of research and renewing a long-standing debate among researchers about just how large disparities of language and vocabulary are among different social classes—and how much those differences matter, if at all.

The new study, which was published in the peer-reviewed journal Child Development, reflects the findings of a group of researchers who over the course of two decades studied nearly four dozen families across five different geographic locations in the United States. Three of the communities studied were urban while one was rural; two communities were poor, one was middle class, and two were working class. (One was African American, and the rest were European American.) As with the 1995 study, the researchers recorded conversations between parents and their children, counting the number of words and conducting other linguistic assessments. But they also analyzed the words spoken by all of a given child's caregivers to that child, as well as those spoken between other people within earshot, even if not directed at the child—an exchange between a parent and older sibling while the child was in the room, for example.

Douglas Sperry—the lead researcher and a psychology professor at Indiana's Saint Mary-of-the-Woods College—and his colleagues didn't find a correlation between the socioeconomic status of a child's family and the number of words that child hears. "There is a lot more language going on in the homes of [low-income] people … than the Hart-Risley study suggests," Sperry said. The results were all over the map, with lots of variation within each socioeconomic level.

Other scholars and activists have also critiqued the original word-gap study's methodology and the way its findings have been interpreted by policymakers. Critics say that policies that grew out of simplistic interpretations of this study were racist, classist, and simply ineffective. Some policymakers and education reformers, they said, blamed parents for the academic gap, instead of acknowledging the other forces at play.

One linguist, Michael Erard, noted in a 2014 Atlantic article that "just as solving climate change isn't about closing the polar bear gap, and preventing environmental degradation isn't about closing the tree gap, you can't increase children's school readiness by closing the word gap." One 2017 study published in the Harvard Education Review even found that the word-gap research had the unintended consequence of perpetuating negative stereotypes about the children of Latino immigrants, with teachers in classrooms serving such students resorting to less-sophisticated instruction.

Critics are now taking aim at the methodology of Sperry's study. Some experts question the value of Sperry's focus on overheard speech, pointing to research that has found that young children learn best from speech directed at them and not from overheard speech. Some critics also note that the study excluded high-income families, which makes a direct comparison to the original word-gap study more difficult. Sperry and his team have responded to these critiques, citing research to suggest that overheard language does play a role in language development, and arguing that the lack of high-income parents in the study doesn't negate their finding that their poorest groups outperformed the welfare group in the 1995 study.