|The Secret of the Staffroom > Is it just a dream?|
Per the Inception top reference, how do we know if William is just dreaming he's a teacher, or is he really a teacher in the future?
For the answer, we look to the stars. Here is the Astonomy test he is marking in the teaching scene.
As you can see, the test is set in the future. So you'll have to wait until an astronaut lands on Mars or until the end of 2030 to see if it is reality (the test question is correct) or if it is just a dream.
In the meantime, here are some articles about it