Ballakermeen High School has asked that Year 9 pupils stay at home today (Friday).
Head teacher Adrienne Burnett has written a letter to students and parents on the situation.
She said: ‘Staffing absences remain very high and have increased as the week has progressed.
‘We will have 30 colleagues absent tomorrow.’
Year nine pupils are aged 13 and 14.
Mrs Burnett said the school had hired as many supply teachers as available.
Ballakermeen will also be doubling up classes, putting a teacher and an administrative support colleague in together.
‘But there are still too many classes requiring cover,’ Mrs Burnett said.
She continued: ‘All of year 9 have a double PE lesson tomorrow, plus a double lesson of design and technology. Although we cannot easily set a meaningful PE lesson, there will be work on Google Classroom from the DT teachers.
‘Please accept my apologies, this is very much a last resort’.
Most of the island’s secondary schools have had to ask pupils to stay at home over the last 10 days because of problems with staff absence.