Thousands of children in the U.K. won’t be returning to their classrooms this week because their schools are at risk of collapse from crumbling concrete.

More than 100 schools were told last week — days before the start of the new school year — to shut some or all of their buildings because they contain a type of lightweight, air-filled concrete widely used in construction between the 1950s and the 1990s.

British Education Secretary Gillian Keegan added on Monday that hundreds more school buildings might also be unsafe due to weak concrete.

School officials are scrambling to find classroom space in nearby facilities or resorting to online instruction after the government’s last-minute directive, sparked when three schools previously thought to be safe suffered collapses over the summer.

Keep reading on cbc.ca