Teachers should surrender one week's holiday a year, a think tank has suggested.
The Centre for Scottish Public Policy said this would minimise disruption to families caused by in-service training days and create potential cost savings.
Leaders of the EIS teaching union said staff already facing a pay freeze and a review of their employment conditions would be unhappy about the proposal.
Teachers are entitled to 13 weeks (65 days) holiday a year.
The CSPP said that could be reduced so that teachers' five in-service days can be concentrated into a single week, at the end of the summer term.
The proposal may appeal to parents who struggle to find childcare for five days spread over the year and there could be a saving on the cost of the temporary staff who sometimes cover for teachers on courses.
But there is concern that the plan could diminish the goodwill in schools which ensures many staff go the extra mile for pupils.
An EIS spokesman said: "Teaching staff are already facing the imposition of a pay freeze for the next two years, together with a review of their employment terms and conditions.
"Any further moves which could lead to poorer working conditions for teachers would be a disincentive to many people who are considering a teaching career.
"It is essential that high-quality graduates continue to be attracted into teaching, but in order to do this it is important that appropriate salaries, terms and conditions and professional development can continue to be offered."