Gerard was one of those difficult pupils who you really had to humour. It was an English lesson and the subject was animal rights. “My grandma used to have a chimpanzee as a pet,” said Gerard.

I remembered that Gerard lived with his Gran as his acting parent and impulsively suggested Gran should come in to talk to the class about her experiences with her pet chimp Monty. Never having met Gran did not seem a huge problem to me and it was agreed that she would come in the following week.

The next week, I was met by an extremely large lady and, judging by her breathlessness, I realised she would take ages to mount the stairs. She would need to sit throughout the talk, and our little school chairs would be totally unsuitable. With much coaxing, Gran eventually made it. I dashed in and quickly opened the windows as Gran’s hygiene left a lot to be desired.

Gerard sat, proud as punch, until she started her monologue. Suddenly, every description of life with Monty was compared by Gran to life with Gerard. Little red-headed Gerard was getting properly wound up. Embarrassing tales oozed out of Gran’s mouth. I kept trying to ask questions that would be totally unrelated to red-faced Gerard, but Gran was having none of it.

The class went from shocked silence to hysterics. How could I get rid of the woman? Suddenly, the fire bell saved us - there must be a God.

I assured Gran it would not be fair to let her climb the mountain of stairs again and we sent her on her way. Shortly after, I heard Gran had a new pet - a snake - but I decided to hold back on that one.

The writer is a teacher in North Yorkshire. Send your worst parent stories to features@tes.co.uk and you could earn #163;50 in MS vouchers.