The Scientific Advisory Group for Emergencies advised the Government to improve ventilation in schools in May 2020. It warned the Government to prepare for winter in July 2020. More than 10 million days of in-person teaching were lost last term. More than 400,000 children were out of school with covid last week. A quarter of schools faced teacher absences of 15% or more. Air cleaning devices are more than 18 months late, and are being offered to fewer than one in 30 classrooms. Why did Ministers ignore the advice about the importance of ventilation in schools for so long?