The school self-developed e-learning platform can provide students with real and non-real-time learning resources based on its personalized learning properties like self-owned teaching conditions and levels. Meanwhile, it is beneficial to students' independent study and academic performance. During the COVID-19 pandemic, schools in China adopted e-learning platforms to conduct online teaching, whereas the efficacy of these online teaching platforms was not definitely known. It is necessary to review their effectiveness, especially for those developed by schools themselves. A total of 417 of 7th and 8th graders from two middle schools in Nanjing, Jiangsu Province were enrolled with 208 in the experimental group and 209 as the comparisons. The primary outcome of the study was students' academic performance. The results demonstrated that: (i) the online platform-based self-learning was conducive to students' grades; (ii) school self-developed e-learning platform was more effective in improving student achievement than other non-school self-developed ones.