The present investigation assessed the effects of an extensive viewing treatment (11 captioned episodes of an animated cartoon) on the learning of 36 target words by means of a pretest and an immediate posttest in a group of 120 primary school learners (years 4 and 5; aged 9–11; L1 Spanish-L2 English). More specifically, students’ vocabulary gains were assessed at the level of written word form recall, and form-meaning link recognition. In addition, considering the variability in gains among target words, this investigation explored the impact on the outcomes of word-related factors (i.e., orthographic regularity, length, concreteness) and a context-related factor (i.e., frequency of occurrence in the input). The results revealed that the participants obtained significant vocabulary gains, especially at the level of form-meaning link recognition. In addition, fifth graders were found to obtain higher gains in comparison with fourth graders, suggesting that the older group was better equipped to pick up words from the input. The extent to which word- and context-related factors influenced the results depended on the specific word knowledge dimension under study. While the recall of written word forms was found to be affected by orthographic regularity, length and concreteness, the recognition of form-meaning links was moderated by length, concreteness and frequency of encounters.