The head at Castle Rushen High School, Maria Tomaszewska, is absent from her post - on the first day of the new term.
There's no official word as to why - or when she's likely to return.
However, it's understood the Department of Education is to appoint an Acting Head for the secondary school.
The deputy heads Peter Teare and John Binns are today in charge at Castle Rushen.
Neither is able to comment on the head's absence and the Department says it's not able to discuss internal employment matters with the media or the public.
In a statement, it says as far as students are concerned, life at school will continue as normal. And the Leadership team will continue to manage the school pending the appointment of an acting headteacher.
Mrs Tomaszewska's leadership style has been subject to criticism - earlier this year a special inspection was ordered, which highlighted poor communication and lack of consultation between senior leaders and staff.
Last month, Castle Rushen celebrated superb A level results - placing the school among the top handful of state comprehensives in the UK.
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