US-based Bruce Perry said they were partly responsible for an unravelling society in which people were "turning on each other".
Dr Perry, whose experience has included working with young victims of the September 11 terrorist attacks, took his uncompromising message to teachers and other professionals in Edinburgh last week.
"The human brain is not designed for the modern world," he commented. Human beings were social creatures, but now lived in an "invented environment" which left children growing up with a "poverty of relationship", said Dr Perry, who is based at the Child Trauma Academy in Texas.
Schools were symptomatic of this wider problem, he added: even a teacher with a class of 20 could not hope to meet the needs of all pupils. The only choice was to "teach to the mean", with the result that high-fliers and strugglers were poorly served.
He had seen "therapeutic pre-schools" for aggressive and out-of-control three- and four-year-olds, where there were 22 children to one staff member. This marked a sudden and drastic change: for much of human history, children had been accustomed to having four significant adults around them.
"We've gone away from a relationally-rich environment," Dr Perry said.
The well-intentioned efforts of parents, educators and other professionals missed this crucial point: policy, practice and law were "very disrespectful" to fundamental human biology, he claimed.
Dr Perry did not excuse himself from this observation, admitting that he had "participated in the failure of hundreds of thousands" of children.
The result was that "social fabric frays", amid increasing cases of violence and illness. "When the fragile social and emotional bonds that keep human beings together dissolve, we turn on each other," he said.
The human brain needed a "reward" every seven or eight minutes, Dr Perry went on, and these largely came from human-to-human interactions. Even a subtle exchange between an adult and a child that lasted three seconds was a "meaningful physiological act".
He went on: "Everyone needs their reward bucket filled up, but if you don't fill it with relational stuff, you fill it with other things."
Dr Perry, who has also counselled traumatised victims of the Columbine school shootings, the Waco siege in Texas and the Oklahoma City bombing, explained that the brain did not like surprises.
Novelty was stressful, but "the key is to stress the right amount", he said, adding that children he worked with often had a "deregulated stress response system".
Something that would be a minor stress for most, such as a school test, puts them in an "alarmed state". Even well-prepared teachers were destined to struggle with traumatised children, because their brains had not developed as they should.
Dr Perry spoke to a wide range of education and other professionals from across Scotland at a conference in Edinburgh. It was organised to mark three years of the city council's Growing Confidence project, which aims to boost the confidence of entire communities.