The fluid-filled balls, which attach to a child's finger with a rubber string, were banned by the Department of Trade and Industry last week.
Tests revealed that the toy failed to meet safety requirements, after eight children were nearly strangled when the ball's string wrapped around their necks.
Roz Marusiak, assistant head of Alderman Richard Hallam primary, in Leicester, agreed that the toys posed a serious risk. She said: "I thought they were lethal when I first saw them. Children could be hit in the eye or the head. We'd already had tears."
Many schools had already banned yo-balls from their playgrounds. Janet Saunders, head of Henwick primary, in the London borough of Bromley, banned the toy the first day it appeared at school. She said: "Children were hitting each other round the head, and being thorough nuisances with them.
I just saw them as a very unuseful missile."
But not everyone is so happy at the ban. Melanie White,11, from Ipswich was so incensed that she wrote to the Daily Telegraph, pointing out that the packaging clearly says "do not swing round neck or it will cause a choking hazard'. I don't think its fair that I can't use it," she writes.