The unofficial version: being cannon-fodder for a classful of rowdy kids. Check out this children’s poem by Allan Ahlberg:

The Supply Teacher

Here’s the rule for what to do

If ever your teacher has the flu

Or for some other reason takes to her bed

And a different teacher comes instead

When the visiting teacher hangs up her hat

Writes the date on the board, does this or that

Always remember, you have to say this,

OUR teacher never does that, Miss!

When you want to change places or wander about

Or feel like getting the guinea pig out

Never forget, the message is this,

OUR teacher always lets us, Miss!

Then, when your teacher returns next day

And complains about the paint or clay

Remember these words, you just say this:

That OTHER teacher told us to, Miss!