To what extent are research results influenced by subjective decisions that scientists make as they design studies? Fifteen research teams independently designed studies to answer five original research questions related to moral judgments, negotiations, and implicit cognition. Participants from 2 separate large samples (total N > 15,000) were then randomly assigned to complete 1 version of each study. Effect sizes varied dramatically across different sets of materials designed to test the same hypothesis: Materials from different teams rendered statistically significant effects in opposite directions for 4 of 5 hypotheses, with the narrowest range in estimates being d = −0.37 to + 0.26. Meta-analysis and a Bayesian perspective on the results revealed overall support for 2 hypotheses and a lack of support for 3 hypotheses. Overall, practically none of the variability in effect sizes was attributable to the skill of the research team in designing materials, whereas considerable variability was attributable to the hypothesis being tested. In a forecasting survey, predictions of other scientists were significantly correlated with study results, both across and within hypotheses. Crowdsourced testing of research hypotheses helps reveal the true consistency of empirical support for a scientific claim. Public Significance Statement Research in the social sciences often has implications for public policies as well as individual decisions-for good reason, the robustness of research findings is therefore of widespread interest both inside and outside academia. Yet, even findings that directly replicate-emerging again when the same methodology is repeated-may not always prove conceptually robust to different methodological approaches. The present initiative suggests that crowdsourcing study designs using many research teams can help reveal the conceptual robustness of the effects, better informing the public about the state of the empirical evidence.