North Lanarkshire, the second most deprived area in Scotland after Glasgow, according to the Scottish Office's "poverty index", says that additional teachers allocated to "areas of priority treatment" have been deployed on the basis of out-of-date information from the 1981 census.
A review using the more precise measure of clothing and footwear grants discovered that 91 per cent of pupils at Castlehill primary in Wishaw received these allowances but the school was not classed as eligible. At the other extreme, some deprived areas had pockets of affluence within them.
Following the review, approved by the full council on Tuesday, 115 primaries out of 134 and all 26 secondaries are to receive extra staffing help. Currently 46 primaries and 17 secondaries are involved.
"We discovered that using the clothing grants unveiled more widespread poverty which is not confined to tight geographical areas," Christine Pollock, North Lanarkshire's depute director of education, said.
Around 20 primaries will lose teachers as a result of the changes. There is also a proposal to save cash by easing out 26 senior primary teachers and five senior secondary teachers. But the savings would be "relatively small" and and only available as posts fell vacant.
Ms Pollock said redeployment of staff to schools in deprived areas would now be carried out as part of the annual staffing review. "The use of clothing grants as an indicator of need means we can respond more quickly to schools' fluctuating requirements instead of waiting for census information," she stated.
Meanwhile, South Ayrshire has taken a similar step, increasing the number of schools entitled to extra staffing from eight to 17 by basing the formula on footwear and clothing grants.