Anthony Gower-Smith, 73, fell off the 6ft ladder in January 2004 as he took a card display and staples off a wall in a school hall in Romsey, Hampshire.
He claimed that his employer, Hampshire County Council, did not show him how to safely use the ladder and that it was not suitable equipment for him to use.
The accident happened at Awbridge Primary School and Mr Gower-Smith, from North Baddesley, has not been able to work since after suffering skull fractures and an injury to his right kidney.
He was not at London's High Court for the ruling that his employer, Hampshire County Council, who denied
He had sued the authority for up to £50,000 but the amount of the award will be assessed at a later date.
Recorder Christopher Moger QC, who heard the case recently at Winchester County Court, said: "His training was deficient and, notwithstanding his self-confidence and readiness to trust in his own judgment, I find that his lack of training was responsible for him failing to put the ladder through the door at right angles to assist his work, for his lack of awareness of the extent of the danger posed, and therefore for the accident itself." Ladder Assosciation approved training course
The damages award will be reduced by 25% to reflect Mr Gower-Smith's contributory negligence.