The aim of the study is to determine the effectiveness of Flexible Learning using the three (3) online teaching platforms: (1) Sultan Kudarat State University Electronic Learning Delivery System (SKSU ELEADS); (2) Facebook Group; and (3) Google meet. In the study, descriptive and experimental method was adapted. In descriptive side, where one hundred thirty-eight (138) respondents, a Bachelor of Elementary Education (BEED 2-All Sections) of College Teacher Education(CTE) of Sultan Kudarat State University (SKSU), First Semester, Academic year 2020-2021. The respondents are randomly selected for online survey through Google forms for the Flexible learning in terms of three (3) qualities; Content, Technical and Instructional. In Finale, where the effectiveness of flexible learning is through pre and post-test scheme of almost one month, discussed the chapter 1 of the subject -EDDMATH 2 entitled 'Teaching strategies of Intermediate mathematics' as one major subject of the proponents. The data were analyzed via descriptive mean, comparison of mean and ANOVA as statistical analysis of this study. The results revealed that the difference weighted mean between the pre-test and post-test is 10.16, which signified a clear graphical presentation of positive skewed in all respondents, which signified the effectiveness of flexible learning. In terms of qualities of three (3) online learning modalities like FB Group, Google Meet and SKSU ELEADS, where Google Meet got a highest mean of 3.68, as indicated that respondents need an interactive discussion even though there is no Face to Face(F2F), due to COVID-19 pandemic era. Among the three (3) online learning platforms, Facebook Group(FG) got F (7,6) = 9.617, p < 0.05 and significantly liked among the respondents due to easy accessibility in rural areas.