Children labelled "average" by teachers are missing out because more focus goes on those at the bottom of the class, a report has found. 

Experts say children who are classified in the middle range risk having late-blooming ability ignored as teachers assume they are neither struggling nor overachieving. 

They said most pupils show either notable promise or are the the lower half of the ability range in a particular subject area and categorising them simply as the "middle" risks ignoring this. 

The report, by testing company GL Assessment, found that "poor verbal, quantitative or spatial skills often mask potential". 

Shane Rae, head of publishing at the firm, said: "Our analysis shows that within the cohort normally identified as ‘average’ (the middle half of students), six in ten exhibit some kind of verbal, quantitative or spatial ability bias. 

"If teachers know exactly what this is, they can then tailor interventions accordingly."

Beccie Hawes, head of Rushall’s Inclusion Advisory Service, which provides advice to help schools include pupils with special educational needs, added: "‘Average’ can be misleading as it may stop us from identifying pupils that are either beginning to experience difficulties as their coping runs out or identifying pupils that are making perhaps accelerated progress."

Poppy Ionides, an educational psychologist, who contributed to the report, said: "A large body of evidence suggests long-term benefit from a ‘growth mindset’ in which children believe in the possibility of cultivating their abilities. 

This feeds perseverance and resilience; failures are seen as opportunities to learn rather than diktats of inescapable ineptitude; those who start ‘average’ have the ability to be all but. Schools have the power to influence children’s mindset."

The study is based on data gathered from 24,500 students who took a "cognitive abilities" test provided by GL Assessment at the age of 11 or 12 and compared with their GCSE results.

Around 50 per cent of youngsters - about 13,400 - were identified as "average" or "middle 50 per cent" in terms of overall cognitive ability test performance.

Among the children considered "average", their chances of getting at least a B in GCSE English varied from one in 10 to seven in 10, depending on how strong their verbal skills were.