Prior to her lesson, the teacher from Staffordshire had repeatedly dropped one of the apples on the floor, bruising its flesh but without damaging the outside.
In class, the children discussed how both the apples looked the same on the outside - both red and a similar size.
"I picked up the apple I'd dropped on the floor and started to tell the children how I disliked this apple, that I thought it was disgusting, it was a horrible colour and the stem was just too short," the teacher wrote on a post on the Relax Kids Tamworth Facebook page.
"I told them that because I didn't like it, I didn't want them to like it either, so they should call it names too.
"Some children looked at me like I was insane, but we passed the apple around the circle calling it names, 'You're a smelly apple', 'I don't even know why you exist', 'You've probably got worms inside you'."
With the kids still unaware what was going on, the teacher proceeded to pass around the other apple and asked the kids to say kind words about it.
The children called the apple "lovely", with "beautiful skin" and a "beautiful colour".
The teacher continued: "I then held up both apples, and again, we talked about the similarities and differences, there was no change, both apples still looked the same.
"I then cut the apples open. The apple we'd been kind to was clear, fresh and juicy inside.
"The apple we'd said unkind words to was bruised and all mushy inside."
The teacher said there was a "light bulb" moment for the children immediately.
"They really got it, what we saw inside that apple, the bruises, the mush and the broken bits is what is happening inside every one of us when someone mistreats us with their words or actions," she wrote.
"When people are bullied, especially children, they feel horrible inside and sometimes don't show or tell others how they are feeling.
"If we hadn't have cut that apple open, we would never have known how much pain we had caused it.
"More and more hurt and damage happens inside if nobody does anything to stop the bullying. Let's create a generation of kind, caring children.
"The tongue has no bones, but is strong enough to break a heart. So be careful with your words."
The teacher's post was shared nearly 80,000 times on Facebook, garnering an impressive 72,000 likes and 8,000 comments, all in just 18 hours.
Commenters praised her "innovative" way of illustrating bullying to children.