More school strikes have been planned in a dispute over pay for support staff, a union has announced.
Unison sent a written warning to Cosla and the Scottish government on the day students returned to their classrooms.
Schools in 24 council areas were closed for three days this week, after Unison rejected an offer from Cosla, the umbrella body for Scotland's local authorities.
Cosla said it had already "made every effort to avert the strike".
The Scottish government freed up £80m so Cosla could make the improved offer, which includes a rise of about £2,000 a year for the lowest paid.
Unite and the GMB suspended strike plans while members were consulted.
The dispute is over a pay offer for non-teaching school staff including janitors, canteen workers, classroom assistants, cleaners, admin staff and nursery staff.
Unison said more than 21,000 of its members in 1,868 schools walked out during the three-day strike.
