The research examined teachers' perceptions of factors affecting their perceived effectiveness in online teaching in the Israeli educational system, comparing Jewish and Arab teachers' views during the Covid-19 crisis. The research employed quantitative and qualitative approaches. 295 teachers responded to a questionnaire, and 22 teachers participated in a semi-structured interview. Quantitative data analysis found that the variables socio-economic status, the teacher's age, technological competence, frequency of synchronous teaching and their satisfaction with the profession significantly predicted perceived effectiveness in online teaching. Comparison between Jewish and Arab teachers indicated the correlation between sector and perceived effectiveness in online teaching is mediated by the number of teachers' synchronous teaching hours. Above all the variables, Jewish teachers' perceived effectiveness in online teaching is best explained by the number of synchronous teaching hours. Jewish teachers taught on average more synchronous online hours per week in comparison to Arab teachers, and the number of synchronous teaching hours predicted perceived effectiveness in online teaching. Quantitative and qualitative data, gathered from the interviews with the teachers were triangulated, reinforcing findings and explaining the quantitative data. Findings revealed that the transition to online learning may increase extant gaps between Israeli society's sectors.