If you can find the Ofsted report about dealing with knives brought into schools in London you will see the response of schools varies a great deal. (I know Watford isn’t London but it’s a good piece of research).
Some schools permanently exclude with virtually no investigation at all and Ofsted are somewhat critical of that. They point out that most DC bringing knives into school are vulnerable and fearful. They are often from deprived families and need a lot of support in their lives. They find that some schools have a greater understanding towards the “crime” and they certainly don’t immediately exclude. They look at all the circumstances which have led to this child bringing a bladed implement into school and what the child actually did.
Therefore the school could have contacted the safeguarding team and did not have to call the police. It would totally depend what the child had done with the knife. Although in primary, safeguarding might have been more appropriate.
What was startling to read was that schools don’t have policies on knives in school. They don’t follow any guidance from their academy chain or LA. They seem to decide what to do on an ad hoc basis. Therefore I think it’s vital schools have sound policies on blades in school and that the government lays down expectations of schools.