It’s almost four years since the world’s classrooms were shut for 16 billion pupils as Covid spread.
The full effects of those policies are only just beginning to be understood.
Data from tests in maths, reading and science on December 5 by the OECD offer the best snapshot of how children were affected.
In many countries, on average, pupils in the rich world scored 10 points lower in reading and 15 points lower in maths than was the case in 2018.
A decline of that magnitude is a calamity.
What the tests implied is that because of the pandemic, pupils missed out on between a half and three quarters of a school year.
A dip in such grades can have dramatic effects for youngsters who fail to graduate from high school.
Degree holders in rich countries earn roughly 50 per cent more than those pupils whose jobs are straight out of school. The OECD countries have run these tests mostly every three years for two decades now under its Programme For International Student Assessment better known as PISA.
In places recording the steepest drops, the PISA tests found 15-year-olds in reading, maths and science were performing at levels in 2018 typical of pupils a full year younger.
A decline of that magnitude was found in many countries including France, Germany, Poland, Norway, Brirain, Australia and New Zealand, even Finland (reputed pre-Covid to have the best education systems on the planet) as just a few examples.