There is ongoing debate over the usefulness of and need for attention checks in online experiments. This paper investigates the value of these tests in decisions‐from‐experience (i.e., multi‐trial repeated choice) tasks. In five studies (Ntotal = 1519), we comprehensively compared the behavior of attentive and inattentive participants (i.e., those who passed or failed a simple attention check) among online participants; and also compared those results to the results of lab studies reported elsewhere. We found meaningful differences between the behavior of attentive and inattentive participants even at the first trial. Overall, attentive participants were more likely to notice less‐obvious average values of the different alternatives, while inattentive participants exhibited higher sensitivity to typical outcomes. The findings show that even one simple attention test is sufficient to differentiate between attentive and inattentive participants in repetitive tasks. Importantly, our results fully replicated three previously run lab studies among attentive participants, but not inattentive ones. This finding highlights the importance of using attention tests to avoid spurious conclusions.