The City of London Academy in Bermondsey is closed to pupils in years 7 to 9 for the next three days due to staff shortages.
A message on the City of London Academy website blames the "current disruption to airline schedules" for the decision to close the school to pupils in years 7, 8 and 9.
Many London schools have been affected by the cancellation of flights caused by the volcanic ash cloud with teachers unable to return from their Easter holidays.
The summer term started as normal on Monday morning for older pupils taking GCSE and A-level exams this term.
Younger pupils will enjoy an extended Easter holiday for the next three days.The school is expected to open to all pupils on Thursday 22 April.
• Do you know of any schools, businesses or services in SE1 that have been disrupted by the volcanic ash cloud? Let us know!