Question

what had once happened to Tommy's teacher

Answer 1

Tommy's teacher faced a small obstacle once which was unexpected.  

Explanation:

Tommy had virtual machines to teach him instead of physical human teachers. Tommy and Margie called the machines as Mechanical teachers. They had a screen which gives test and feedback to the students; they also stored lots of information, unlike the conventional textbook.

The machine had some technical issue and blanked out for unknown reasons. So it was taken away from him to be repaired. It took a month for the repair, and he did not have history classes for a month.

Answer 2

Answer:

Tommy's mechanical teacher broke down. It was taken away for a month because its history section had blanked out completely.