Adolescence and boredom can turn pupils off learning for three years in early secondary school, suggests a study.
The overwhelming majority of pupils start secondary school with "initial enthusiasm" but this wanes during the first two years, figures suggest.
The proportion who "feel good about school" falls 10 percentage points to 84% between ages seven and 14, suggests a GL Assessment poll of 32,000 pupils.
Head teachers' leaders said schools were working hard to address the issue.
"While a whole host of factors come into play at this point in a child's development - hormones, friendships, growing up, taking control - the transition to secondary school marks a significant change for students and it is at this point that we begin to see a change in their attitudes," say the authors.
This decline is important because a positive attitude to learning is crucial to attainment, they argue.
The effect is long recognised by experts - last year, an Ofsted report into the early years of secondary was entitled "The Wasted Years".
The new report suggests pupils' difficulties in coping with a larger school, up to 10 different subject teachers and a more complex curriculum, can last well into Year Nine - the third year of secondary school.
The survey, carried out in the year to April 2016, among 31,873 primary and secondary pupils in England and Wales, found most of the fall in positive attitudes happened after Year Seven.
And a third (32%) of Year Nine pupils said they were bored at school, compared with 19% of Year Threes.
By contrast, the figures also revealed that children responded well to the more demanding secondary curriculum and also felt more confident about their abilities to tackle new work.
Suzanne O'Farrell, a curriculum and assessment specialist with the Association of School and College Leaders, who contributed to the report, said some schools were reversing the dip by giving the first two years of secondary "a very high profile and investment" as "the bedrock of later learning".
"It's about really making sure that pupils are resilient independent learners, able to react independently to feedback.
"All those things should be embedded," Ms O'Farrell told the BBC.
Year Nine then becomes an "acceleration" year to inject a new challenge, before the examination year: "In this way momentum is sustained throughout each phase through new expectations and priorities," she argued.
Paul Foxton, assistant head teacher at Ashlawn School in Warwickshire, told the researchers that secondary transfer can be tough.
"They might have been the top of the class in primary school and performing in the middle of the class now and that can hit some students very hard."
Mr Foxton agreed building resilience was key
"We need to build grit and determination and talk about how everyone needs to make mistakes to learn more effectively," he argued.