This study explores the relationship between teacher teaching support, student involvement, technical environment support, and online teaching effectiveness among K-12 students from the perspective of teaching systems (teacher teaching support, student involvement, and technical environment support) and the differences between online teaching methods and school levels, to provide guidance for teachers to teach using different online teaching methods and at different school levels. The data came from 13,225 primary and secondary school students who participated in online teaching in a district of Beijing. This study used the quantitative research method, we established a model of factors influencing the effectiveness of online teaching through Structural Equation Modelling, and analysed the survey data to explore the factors influencing the effectiveness of online teaching, the paths and their mediating effects. It is worth noting that this study found that student involvement and teacher teaching support significantly and negatively affected the perceived learning effect; teacher teaching support significantly and negatively affected continuance intention; and that the effects of teacher teaching support, student involvement, and technical environment support on satisfaction and the effects of student involvement on continuance intention showed significant differences. These differences affect related mediated pathways, resulting in significant differences in them. In addition, we found that "teacher teaching support [right arrow] student involvement [right arrow] perceived learning effect" was different from "teacher teaching support [right arrow] technical environment support [right arrow] perceived learning effect." We also found a masking effect for the "teacher teaching support [right arrow] student involvement [right arrow] perceived learning effect" and "teacher teaching support [right arrow] technical environment support [right arrow] continuance intention" pathways. These findings provide suggestions for teachers at different levels to design appropriate online teaching strategies to improve student learning.