Teachers and officials at a coed British school were shocked to see a class with an all-boy attendance on the first day of school.

For the first time since it opened 30 years ago Bassetts Farm, a primary school with a population equally split between girls and boys, suddenly had a class of 20 4-year old boys, an occurrence that is still puzzling people.

"Nobody can work out how it happened, it's pretty incredible." said head teacher Christine Jones.

Looking back on her 16-year tenure as a teacher, Jones "I've never known anything like this. Maybe it's something in the local water."

According to Telegraph, Jones said there had been some instances when boys outnumbered girls in a class, "but never all the same sex. It just seems to be one of those freakish things."

The school holds a population of 35,000, making an all-boys class, according to Jones, "a million to one chance - it's like winning the lottery."

The Daily Mail reported that the school would be celebrating its 30th anniversary, according to Jones, who added "it is the first time the foundation class has not had any girls. It is a record for us and probably unusual among other schools."

When asked about how the students are in terms of behavior, Jones commented that "they are not a bad little group of boys but they are boys."