Alice, the first baby, was born on July 31 and eight boys and three more girls followed between September and December.
Sociology teacher Sian Mantovani, whose son Louie was the last to be born, said: "There were lots of jokes about the water supply.
"There have been a lot of nervous people around college. They don't want to catch whatever epidemic we've succumbed to."
Stephen Pegg, the principal, said he did not mind finding maternity cover for almost an eighth of his staff and suggests Ofsted may have been a catalyst for the baby boom.
"We had an inspection about 10 months ago, so maybe there was a lot of relief around afterwards," he said. Alistair Burr, psychology teacher and father of Alice, denies he is the trendsetter. "I don't think I've had any bearing on my colleagues getting pregnant," he said. "I teach social science, so I see it in terms of social trends. It's to do with the age profile."
By the time Lorraine Yates, head of modern foreign languages, told Mr Pegg she was expecting twins Eleanor and Benjamin, who were born in October, the epidemic had reached comic proportions.
But she said: "We were able to share stories about morning sickness, and talk about where to get maternity clothes from."
There were also some concerns. The first baby born weighed eight pounds, the second nine pounds.
"I was terrified," said Ms Mantovani. "The babies seemed to be getting bigger and bigger. I was worried mine would be getting on for 11 pounds."
Mr Pegg hopes that one day some of the babies will be pupils at the school.
"Of course, I will have retired long before then," he said. "Or maybe I will have opened a maternity unit."