Pepe Di’Iasio, head teacher at a school in Rotherham and general secretary of the Association of School and College Leaders, told Today that he believes pupils are being used “as a political football”.
Teachers “want well-informed and evidence-based decisions”, he said, and not “politicised” guidance.
“All head teachers have to assess their curriculum and move their curriculum in order to cope with whatever might be the issue of the day.
“Whilst we welcome a chance to look at this, we also need the flexibility to respond to whatever those particular needs are,” he said.
In a separate interview with BBC News, Mr Di’Iasio added: “Ten years ago, there was no need to teach about sexually explicit images being shared on social media. And three years ago that might have been delivered at age 14, or 15. And now, we’re having to deliver that at age 11 or 12.”
The National Education Union, the UK’s largest teaching union, agreed primary-school children needed to be able to discuss “with trusted adults” information they picked up online about relationships.
General secretary Daniel Kebede said the government was “seeding doubts” about whether school leaders and teachers thought carefully about how they taught about relationships.