21% of schools 'must act on safety'
A fifth of schools need to do more to keep their children safe, inspectors have warned.
An Ofsted report found that 21% of England's schools are only rated satisfactory at "safeguarding", which suggests they need to make considerable improvements.
But a union leader attacked the definition, saying it was "seriously misleading" to interpret "satisfactory" in this way.
Schools that are rated satisfactory are doing what is expected of them, Brian Lightman, general secretary of the Association of School and College Leaders, said.
The Ofsted Safeguarding in Schools: Best Practice report looked at the best ways that schools can ensure children are, and feel, safe.
It is based on evidence from the 19% of schools that have been judged "outstanding" for safeguarding, as well as a detailed analysis of a small sample of schools.
The report concludes that almost all schools are taking "a careful and responsible approach to their safeguarding arrangements".
But it adds: "On the other hand, safeguarding arrangements in 21% of schools were only satisfactory overall, indicating the need for considerable improvement."
Mr Lightman said: "It is seriously misleading that Ofsted continues to interpret the term satisfactory as the opposite of its dictionary definition. If they mean unsatisfactory they should say so.
"They cannot state that 21% of schools were 'only satisfactory' and draw the conclusion that this indicates the need for 'considerable improvement'. While everyone would like all schools to be excellent or good, when a school is satisfactory it has reached the appropriate standard in terms of safeguarding."