More than one in 10 children begin primary school unable to learn and unwilling to build relationships with their peers, a "disengaged generation waiting in the wings", said the thinktank Demos today in a report.
Researchers said that data from the Millennium Cohort Study showed 66,000 children scored "borderline" or "abnormal" in tests designed to reveal behavioural and emotional problems that are intimately linked to under-achievement at school, risk of truanting, and exclusion.
Poverty stands out among a number of factors, Demos said. Having a parent with a low level of education, a mother who is young or parents with a low income all raise the chance of "poorer behavioural and cognitive development".
The difference between children from the poorest and the richest families is stark, with a fifth of those identified as "starting school without the behavioural skills" coming from the poorest section of society, and only 4% coming from the richest.
Stress also plays a part: expectant mothers who experience high anxiety after 32 weeks are twice as likely to have a child with behavioural difficulties by the age of four, than mothers who did not suffer from tension.
The authors say children lose out because of "disengaged parenting", where home life is characterised by low interest, low expectations, a lack of support and few or inconsistent rules. Around a tenth of parents, it says, can be classified as "disengaged", concentrated in the lower income groups.
The study, entitled Ex Curricula, is published on the same day as the government's quarterly statistics on young people not in employment, education or training (neets). Demos's report says this emerging underclass of pre-school children are more likely to subsequently drop out of the education system and become neets. The current generation of 16- to 18-year-old neets will cost society an estimated £31bn over their lifetime.
"At the moment, we tackle the neet problem with jobs and post-16 training, but we are shutting the stable door after the horse has bolted. We deal with a young person's disengagement from their education when it is already endemic," says Sonia Sodha, head of the capabilities programme at Demos. "The annual cost of the neet problem is more than double the annual spend on Sure Start centres which are about pre-school education".
The report criticises government policy, saying there is a lack of spending on pre-school children and that this budget needs to rise. It proposes a "toddler pupil premium" for Sure Start centres and nurseries - with more money going to those serving children from deprived areas. It also calls for financial incentives for at-risk parents to complete parenting courses, and universal screening by health visitors to catch parents at risk of falling into patterns of disengagement. The report highlights work done by Birmingham city council who have invested £40m in early intervention measures - on the expectation that this will return £102m of benefits.
"We have seen from programmes in the US how effectively these schemes work, and there's plenty of evidence now that the first few years are influential in forming habits later on," said Anne Longfield, chief executive of children's charity 4Children. "I think government policy does recognise this, but it has to move from being a political choice to being enshrined in law."