Maddy reports on metal detectors in school
Police in an area of east London say other kids carrying weapons is one of pupils' biggest fears.
So they're are using some special technology to help children feel safer - arch-shaped metal detectors that all pupils have to walk through.
A few schools in the UK already use them, but this is the first time kids across a whole area being tested.
And the detector goes to a different school each day, so pupils won't know when it's going to be at theirs.
On Tuesday the arch was at a school in Waltham Forest in east London, and every pupil had to walk through it before class.
The arch will catch anyone who's carrying a weapon made of metal, including knives or guns.
No weapons found yet
So far 12,000 kids have been checked and police say they haven't found a single weapon.
To make sure they still can't sneak any weapons in there are police officers at the school gates with the metal detector.