Scott Lee's angry father Michael yesterday told reporters the teacher should be "arrested for child abuse".
The police and education chiefs are now investigating the incident at the Meads Infant School in Milford Haven, Pembrokeshire.
The teacher at the centre of the allegations is accused of using her security pass ribbon to fasten Scott's hands together after another pupil alleged he had hit her.
She is still teaching at the school, but Scott's parents have removed him. His father claims the little boy, who is autistic, is having nightmares over the events, adding "It's awful imagining your child tied up".
Dad-of-two Michael, 43, told The Sun: "I believe the teacher is a threat to children. Scott can be a little unruly, but he's never aggressive or in need of being restrained. He didn't deserve this - no kid does."
A Dyfed-Powys Police spokesman said they were 'investigating'.
Pembrokeshire County Council said it could not comment as a probe was 'ongoing'.
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