Anthony Gower-Smith, 73, claims he was not told how to safely use the 2m ladder. He toppled off while removing staples from a wall in the gym at Awbridge Primary in Hampshire in January 2004, Winchester County Court heard.
Mr Gower-Smith is suing Hampshire County Council for liability and damages of up to pound;50,000.
He said he was only warned not to stand on the ladder's top platform and not to work higher than three metres above the ground.
He said he started working at the school in October 2002 and admitted receiving induction training and ticking a box saying he had received training in using a ladder.
The council denies liability.