NASUWT General secretary Chris Keates said unions were trying to keep the action "pupil and parent friendly", such as cutting down on paperwork.
But she warned the position could change, especially after a report from the teachers' pay review body later this month.
A teacher with six years experience has lost £5,500 through a pay freeze and pension changes, while those in the job for two years had lost £3,500, she said:
Teacher morale is at an all-time low and our research shows that over half are seriously considering leaving the profession.
More top news
Outbreaks of rain across northwestern parts of the UK will move slowly southwards.
The credentials of tens of thousands of government officials, parliamentary staff and police officers are reportedly being traded online.
A Which? investigation showed that users of Virgin Media's Super Hub 2 router could be at risk of a hacking attack.