A fidget spinner is basically a 3-pronged piece of plastic or metal that's small enough to sit in the palm of the hand.
The toy spins around a centrally weighted disc that contains ball bearings to keep it spinning.
The spinner can be balanced on a finger or teamed up with other spinners to make colourful patterns.
Why are spinners popular in schools?
Fidget spinners are being marketed as tools to keep kids' hands occupied and help them to concentrate better – particularly for children who have ADHD or Autism Spectrum Condition (ASC).
The cheapest spinners can cost just a few pence – particularly when bought online – so they are easy to afford with pocket money.
Do they work?
Experts say there is no firm scientific evidence to suggest they can help people with ADHD or similar conditions.
However, autism specialists say many children, young people and adults on the spectrum may benefit from using the spinners if they offer comfort and calm when anxiety levels rise.
Are schools right to ban them?
Many schools have decided to ban fidget spinners from classrooms because teachers found they were disrupting lessons.
"You cannot use them in the classroom because it doesn't help a child focus on the lesson," says Andrea Bilbow, chief executive of The National Attention Deficit Disorder Information and Support Service (ADDIS). "It takes the focus off the lesson and onto the toy; and it becomes a distraction for every other child in the classroom as well."
She says they should never have been marketed as a tool to help behavioural problems. "I've had a parent contacting me saying they've had a letter from the headmaster of their school, banning it from the school but bringing the focus of attention to children with ADHD in the classroom. She felt this was stigmatising because all children were playing with them, not just the ADHD children."
The North-East Autism Society is advising parents to let their child's school know if there is a genuine reason for allowing he or she to take a fidget spinner to school, such as to help relieve anxiety.
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