In the post-pandemic era, online learning has gained significant attention in K-12 schools (primary, secondary and high schools). A critical issue is the uncertain relationship between students' perception of the online learning environment, self-regulation, learning engagement and learning effects. There's also insufficient focus on differences across three learning stages. Therefore, it is imperative to identify the factors affecting student learning effects. This study analyzed online learning survey data from 84 schools in a certain district of Beijing, including 13,225 students. From the perspective of "Pedagogical-Societal-Technological" framework, significant differences across K-12 stages. So by analysis these differences in online learning effects, can further analyze the differences in K-12 school online learning mechanism, recognizing the need for a more comprehensive approach to digital reform in education.