The current study aims to analyse school leaders' understanding and expectation of, and support for, online teaching and learning during and after the outbreak of the COVID-19 pandemic. Based on the theory of reasoned action (TRA) framework, the authors designed a questionnaire and collected 319 responses from school principals about their views on online teaching and learning. Structural equation modelling revealed that principals' understanding was significantly associated with their expectations and support. Together with a thematic analysis, this study indicated that school principals understood online teaching and learning. The most expected item was students' ownership and access to a suitable device for online learning. Principals were willing to support students' self-regulated learning through online teaching. They appealed for more support for the infrastructure needed to ensure teachers' and students' privacy and security in online teaching and learning. They had suggestions for teacher development to tackle learner diversity in the online mode.