The number of schools in England affected by crumbling concrete has increased to 174, new figures published by the government show.
The number stood at 147 as of 30 August, but has increased by 27 as of 14 September.
Officials said surveyors have been checking hundreds of schools every week for reinforced autoclaved aerated concrete, known as Raac.
The government said it would be updating its list every two weeks.
Despite the increase in cases of confirmed Raac, more pupils in affected schools have been able to return to full-time face-to-face education since the first list was released.
A number of schools had to delay their September term restart as the Department for Education (DfE) told them to close areas where Raac was present.
But many of those have now been able to introduce mitigating measures to allow pupils back into school.
MPs are due to question education officials on Tuesday about disruption to schools and colleges.
