Research from West Dunbartonshire, the result of a pioneering partnership with Save the Children, also shows teachers are too remote from agencies which work with poor families.
It comes as a separate Save the Children report, published last week, found that the number of children living in "severe poverty" in the UK was increasing even before the recession struck. About 1.7 million children - one in eight - were affected in 2008, up by 260,000 from 2004. The Scottish figure was 95,000, which is 9 per cent of the child population.
The report on West Dunbartonshire, commissioned by the charity from Strathclyde University, shows that identification of the most vulnerable children often does not involve hard data, with staff relying on "informal chats" instead.
"Most managers and staff talked about using their intuition and observation of children and parents' appearance to identify them," it states. "Information about families was not collected in any systematic way".
The researchers, who focused on children aged four to seven in the Clydebank area, believe the "lack of formal mechanisms to identify families who are vulnerable means that staff could not always give the support needed".
If better use were made of statistical indicators - such as free school meal entitlement, council tax benefits and child tax credits - problems would be picked up earlier.
But teachers and nursery staff often lacked confidence to support families in complicated circumstances, and did not feel they had enough training to do so. They did not tend to see multi-agency work as part of their job, preferring to leave that role to heads. The report stresses that they should view such work as a "matter of routine".
Terry Lanagan, West Dunbartonshire Council's executive director of educational services, said staff were "very skilled" at spotting signs of severe poverty, but agreed this could not take the place of "hard information".
Save the Children has agreed to work with West Dunbartonshire Council for five years, the first time it has struck a partnership with a local authority on such a scale.
It has led to projects such as One Street at a Time, which is examining the educational journeys of children in a neighbourhood straddling West Dunbartonshire and Glasgow, comparing their progress.
Families and Schools together, which stems from the United States and has never been used in Scotland, is another aimed at encouraging families to support each other.
The researchers initially held interviews with 13 people from a range of services. The second stage involved three schools and three early education and childcare centres, including: interviews with heads and focus groups covering 10 teachers, 10 early years practitioners, 25 parents and 26 children.
Meanwhile, in response to the Save the Children national report, the Westminster Government says it has lifted 500,000 children out of "relative poverty", and helped the very poorest, as defined by its own criteria.
Ministers have pledged to halve child poverty by 2010 from the 1998-99 figure of 3.4 million - and end it altogether by 2020.
Henry Hepburn, email@example.com.