Nearly one in five youngsters show signs of doubting their academic abilities and self-worth, according to a study.
Boys are just as likely to have these feelings about themselves as their female classmates, it suggests.
These traits are strong indicators that children's mental health and wellbeing are at risk, the GL Assessment report argues.
The study is based on an analysis of responses given by more than 850,000 seven to 14-year-olds in England, Scotland, Wales and Northern Ireland to questions related to how they feel about themselves and school.
This information was linked to different factors that can indicate issues with a pupil's wellbeing - such as youngsters' own self-regard and their work ethic.
It concludes that 19% have low to moderately low attitudes to "perceived learning capability" - suggesting that they doubt their learning ability, while the same percentage had low to moderately low attitudes for "self-regard as a learner".
In addition, 18% were in these categories for "attitudes to attendance" and 15% for "general work ethic".
"There is little gender variation in most factors - boys are just as 'at risk' and as vulnerable as girls", the report argues, adding that the main exception was that a significantly higher proportion of boys scored poorly for "preparedness for learning" compared with girls.
In a foreword to the report, Greg Watson, GL Assessment chief executive, said: "According to our study of over 850,000 seven to 14-year-olds - the largest of its kind in the UK - almost a fifth of them have negative feelings towards school and struggle with issues like self-regard and their perceived capabilities as learners.
"These often-hidden attitudinal issues can have a big impact on attainment.
"But it's not only academic performance we should be worried about. These negative attitudes are precisely those that practitioners fear put children's wellbeing at risk.
"When you add in other issues, such as a lax work ethic and a poor attendance record, the chances of children becoming unhappy or even ill increase significantly."