The purpose of this study was to explore the influence of the design-quality of current online K-12 learning applications on student learning via three learning-related variables (student enjoyment, motivation, and anxiety level when using those online applications). Nine hundred online K-12 applications (WebQuests, online drills, games, tests and other applications) were evaluated in terms of four design factors (quality of information, design of information, quality of technology use, and design of technology use) in relation to the three learning-related variables. Three prediction models were generated and tested in this study. An intermediate effect was found between the design of online application and student learning, which may provide some insights for teachers when they integrate online applications into teaching and learning. The target audience of this paper may be school teachers, designers, or professionals who use online applications for education purposes.