The extra £1 billion being spent on school buildings still leaves funding "well below" 2010 levels, according to a respected education economist.
The building scheme, described by prime minister Boris Johnson as a "major new investment", will begin in 2020-21 with the first 50 projects targeted towards areas where school building conditions are worst, including in the North and the Midlands.
But the investment follows years of real-terms cuts to the capital spending budget, the main pot of money that funds big school building projects.
Luke Sibieta, a research fellow at the Institute for Fiscal Studies, calculates that if the £1 billion were added to next year's capital spending budget for schools, this would only take funding back to 2015-16 levels.
He said: "Following a £500 million cut in the education capital budget in 2020, capital spending was about one third lower in real terms in 2020 than it was over a decade earlier in 2008.
"If the government managed to focus all the extra £1 billion on 2021, that would equate to just over 20 per cent of planned spending for this year.
"Whilst this is a significant sum, it would still only be sufficient to take spending back to 2015-16 levels and would still be well below its high point around 2010."
A National Audit Office report three years ago found at least £6.7 billion was needed to restore all school buildings to a satisfactory condition. Heads say conditions have worsened in the meantime.