There is no strong evidence that putting twins into different classes at school is better for them academically, according to researchers.

A new study argues that there should be no strict rules on separating twins, and it should be left to the twins, their parents and teachers to decide what is best for them.

It found there was "almost no sizeable positive or negative average effect" of classroom separation on twins.

The findings come in a paper, published in Developmental Psychology, led by academics at Goldsmiths, University of London, which analysed information on more than 9,000 pairs of twins aged between seven and 16 in the UK and Canada.

Researchers looked at twins' academic achievement, based on teacher reports and state exam results, as well as their cognitive abilities and academic motivation.

The study concludes: "Our results show almost no sizeable positive or negative average effect of classroom separation on twins' achievement, cognitive ability and motivation."

It also says that the results "showed almost no average effect of classroom separation, or cumulative effect of separation across years of education".

These results were similar across ages and countries, and among both sexes and both identical and fraternal (non-identical) twins.

It adds that, among the UK twins, the only significant differences between twins taught together and separately was at the age of 16, with a "weak average effect" in favour of educating twins together.

Yulia Kovas, Professor of Genetics and Psychology at Goldsmiths, and lead author of the study, said: "We are not saying that separation has no effect on the children involved but rather that there is no strong evidence to justify a rigid rule that twins should be taught separately - or taught together - because it is better for their academic studies.

"What this suggests is that the decision on how twins should be taught should be discussed between parents, teachers and twins, and reflect the individual needs of twins."