This study investigated three look-up conditions for language learners to learn unknown target words and comprehend a reading passage when their attention is transferred away to an on-line dictionary. The research questions focused on how each look-up condition impacted the recall and recognition of word forms, word meanings, and passage comprehension. The participants were 84 first-year Japanese medical university students. The recall and recognition of word forms and word meanings, and passage comprehension data were analysed using the Rasch model. Probabilities of p<0.05 were considered measurably different for the sample population used in this study, and probabilities of p<0.003 were considered statistically significant and generalizable to a larger population. Overall, the results suggest three findings with regard to the on-line dictionary study. First, if only the results that were statistically significant are considered, there might be two conditions to learn words and comprehend reading passages: the spell condition seems to be best for learning the forms and meanings of words, and the control condition for promoting passage comprehension. Second, if the results that were both statistically significant and measurably different are considered, the spell, click, and control conditions might promote the learning of word forms, word meanings, and passage comprehension, respectively. Third, however, the click condition might promote both the learning of word meanings and passage comprehension because its effects were measurably higher to the spell condition on these measures. The results are consistent with the type of processing-resource allocation model for learning the forms and meanings of words and cognitive load theory for comprehending reading passages.