My year 10 health teacher tried to tell us that twins was 2 sperm and 1 egg. Um no! That doesn't even come close to matching up
I had to explain the difference between the 1 egg 1 sperm that splits forming 2 embryos and the 2 eggs 2 sperm forming non identical twins.
His response "well I didn't look into it in THAT much detail" - common knowledge of a health teacher I should expect!!