Evidence shows that the first component of media literacy to develop in children is media sign literacy (MSL), an ability that focuses on the understanding and correct use of the signs and symbol systems that organize different media. Previous research has shown that MSL is a significant predictor of learning from media. In this study, we investigated the impact of a self-developed tablet-based MSL training on children's knowledge acquisition from educational media. A sample of 144 preschoolers aged 4 to 5 years old either received the training (training group) or did not (control group). The training program was executed over a period of 4 weeks. After the program, all participants answered recognition and inference questions about an educational film and an audiobook to assess their knowledge acquisition. The children's verbal and nonverbal intelligence (both before the training) and MSL (before and after the training) were also assessed. The results showed that the training successfully improved the children's MSL. Further, the children in the training group had significantly higher recognition and inference scores for the film, along with significantly higher inference scores for the audiobook. Regression analyses also revealed that MSL baseline scores (pretraining) predicted knowledge acquisition from the film but not audiobook.