The education secretary has expressed “deep concern” that some children are missing lessons to join protests backing a ceasefire in Gaza, with hundreds estimated to have joined school strikes on Friday. Gillian Keegan said schools should treat the wave of absences “with the utmost seriousness”, despite strike organisers circulating messages suggesting parents would not be fined if children missed school for short or one-off instances. The school strikes have been called by the Stop the War Coalition, which tweeted pictures saying hundreds of children had joined protests outside town halls in Glasgow, and in the London boroughs of Redbridge and Newham. Using the hashtag SchoolStrikeForPalestine, students also staged walkouts in Manchester, Luton, Bristol, and the London boroughs of Tower Hamlets and Harrow. However, Keegan said the movement was not acceptable. “I’m deeply concerned that some children are attending political protests during the school day. “Even more so if they’re taking part in, or being exposed to, antisemitic chants. This should be treated with the utmost seriousness – missing school for activism is unacceptable.” More school strikes are expected next week, and the weekly national marches in London have this weekend been changed to local action by protesters supporting Palestine and calling for a ceasefire in Gaza. Schoolchildren handed in a petition calling for a ceasefire to representatives at Bristol’s city hall, collected by Carla Denyer, the co-leader of the Green party. Speaking in Bristol on Friday, Denyer told protesters: “Thank you for taking a stand for Palestine and for calling for a ceasefire. The abhorrent situation in Palestine and Israel must end. “I know we are all horrified by the Hamas attacks and we all want the immediate release of the hostages. Those atrocities do not in any way justify the level of bombardment of civilians, including many Gazan children, that has shocked the world.” The war in Gaza was triggered after Hamas killed 1,200 people, mostly civilians, in a massacre in Israel and took about 240 people hostage. Israel’s subsequent bombardment and incursion into Gaza has killed an estimated 11,470, about 4,700 of them children, according to the Hamas-run Palestinian health authority. The Stop the War Coalition, an organisation set up to oppose the Iraq war, has issued instructions on organising a school strike, with templates for WhatsApp groups and letters. It has also told local organisers: “We’ve been assured by those working in schools that whilst this would count as an unauthorised absence, a child can have up to four days in a row unauthorised and would need 10 in a short amount of time to be fined. Please do check your own school policy.”