Background: Past research has shown that watching a subtitled foreign movie (i.e. foreign language in the soundtrack and native language in the subtitles) leads to considerable foreign-language vocabulary acquisition; however, acquisition of the grammatical rules has failed to emerge. Aims: The aim of this study was to obtain evidence for the acquisition of grammatical rules in watching subtitled foreign movies. Given an informal context, younger children were predicted to outperform older children in acquiring a foreign language; however, older children will take more advantage of explicit instruction compared with younger children. Sample: In Experiment 1, 62 sixth-graders from a primary school and 47 sixth-graders from a secondary school volunteered to participate. The participants in Experiment 2 were 94 sixth-graders from primary schools and 84 sixth-graders from secondary schools. Method: The two experiments manipulated the instructions (incidental- vs. intentional-language learning). Moreover, before the experiments began, some participants explicitly received some of the foreign grammatical rules (presented rules), while the movie contained cases of presented rules as well as cases of rules which had to be inferred (not-presented rules). Results: Rule acquisition through the movie only was not obtained; there was a strong effect of advance rule presentation but only on the items of presented rules, particularly among the older participants. Conclusions: Contrary to vocabulary, grammar may be too complicated to acquire from a rather short movie presentation.