Substitute teachers don't always know what to expect when they walk into a classroom, so they have to balance confidence, flexibility, and boundaries on the fly. It can be known to be a difficult position, and the interviewer is interested in your ability to navigate complicated classroom circumstances.

Pro tip: you might go a step further and add that you are very intentional about setting substitute teachers up for success with a well-outlined lesson plan. This will show that you are aware of how difficult subbing can be, and you plan ahead to ensure that every day in your classroom is valuable - even when you aren't there.