In the light of Integrative CALL, this research aims to know the effectiveness of using online learning platform like a Learning Management Software (LMS) in teaching writing among ESL students in the absence of a traditional classroom instruction. Through a quasi-experimental approach, the study was able to establish that there was no significant difference between the pre- and post-essay overall writing performance of a group which received writing instruction online and a group which received classroom instruction. However, analysis of the individual scoring components revealed that the online-instruction group did not improve in their content-building skill. Focus group interviews were also conducted to know the strengths and weaknesses of the online-based instruction and it was able to reveal that students consider it to be helpful in acquiring sources and expressing opinions, and convenient for lessening issues about time and fear of direct feedback. However, when it comes to instruction and consultation, the students still preferred the face-to-face classroom dialogue. It was also found how lack of autonomous learning habits can be a hindrance to online-based instruction.