Major disruption is expected next week as members of Northern Ireland's five teaching unions are due to go on strike.
Five days of walkouts have been planned in response to a long-running dispute over pay.
Last week, non-teaching education staff held a day of strike action over failed pay reform and education budget cuts.
A half-day strike will be held on Wednesday 29 November, with a further four days planned for after Christmas.
Head teachers will join strike action for only the second time in their union's 126-year history.
The National Association of Head Teachers (NAHT) previously joined four other unions in a full-day walkout in April.
