Final answer:
When the lights don't turn on and the classroom's breaker is not open, the next step is to develop a new hypothesis for the cause of the problem.
Step-by-step explanation:
The next best step to solve the problem when the lights in the classroom do not turn on and the breaker is not open is to develop a new hypothesis for why the lights don't turn on. This is because checking if other breakers are open would be less specific to the classroom in question, and it would be premature to notify school administrators before further troubleshooting. Ensuring the lights are plugged in may not apply since classroom lights are typically hardwired and not reliant on being plugged into outlets. Therefore, the student should consider alternative reasons for the outage, such as the bulbs being burnt out or an issue with the light switch itself.