The cleverest Scottish schoolchildren are the equivalent of a year’s worth of schooling behind at science compared to before the SNP took power, according damning research.

Think tank the Sutton Trust found that there was no area where the brightest Scottish 15-year-olds “really excel”, with their weaknesses including a “pronounced and sustained decline” in their performance at science since 2006.

Its research concluded that the decline was “equivalent to around a year of schooling” and they were “trailing behind the performance of able pupils in England in most subject areas.”

The study discovered bright children from poor backgrounds in Scotland lag behind their wealthy classmates by more than two-and-a-half years by the time they reach 15.

Clever youngsters from deprived backgrounds were 31 months behind their wealthy peers at mathematics and science and 26 months behind for reading.

Although the gaps were even larger south of the Border, the report found that bright pupils from both deprived and wealthy backgrounds performed better in English schools in all three core subjects.

The study noted with concern that the mathematics skills of Scotland’s brightest children have declined since 2009, two years after the SNP took power.

The Sutton Trust obtained the findings by further analysing the results of last December’s Programme for International Student Assessment (PISA) survey, which caused political uproar.