["Japanese Psychological Research, EarlyView. ", "\nAbstract\nIn this study, we evaluated the effectiveness of full‐argument (subject–object–verb: SOV) sentences versus one‐argument (object–verb: OV) sentences in teaching Japanese object case markers to Chinese‐speaking children learning Japanese as a second language (L2). The findings informed the development of educational materials tailored for learners of Japanese as an L2. The experiment involved 34 Chinese‐speaking Japanese L2 children (aged 6–10 years) who learned the artificial subject case marker po and the artificial object case marker bi using full‐argument and one‐argument sentences. The results revealed that one‐argument sentences were more effective at conveying the use of case markers. Additionally, as the duration of exposure to Japanese increased, children learning their L2 became more adept at learning from one‐argument sentences, exhibiting a pattern similar to that of Japanese‐speaking children. These findings underscore the effectiveness of one‐argument sentences for language acquisition by children and highlight the similarities and differences between first‐ and second‐language learning in children. Based on these results, we developed an application designed to teach object case markers through one‐argument sentences. After these materials were used, children demonstrated improved case marker usage accuracy.\n"]