The tragedy unfolded when the care worker took 14-year-old Callum Garland for a visit to the park opposite Alwoodley Primary School on August 6, 2015.
There he allowed the teenager – who had learning difficulties and was living at the Lingfield Approach children’s home in Moortown – to climb a tree while playing.
Around 10 minutes later he called for Callum to come down and, after getting no reply, climbed the tree himself and found the youngster with a rope around his neck.
The care worker, who is no longer employed by the council, tried to move Callum – who was over 6ft tall – but could not because of the boy’s size.
A new report by the Leeds Safeguarding Children Board says that, rather than immediately contacting the emergency services, he then set off “hurriedly” walking back to Lingfield Approach.
He did not dial 999 until he was told to do so by a colleague – and after getting through, said that Callum only appeared to be stuck in the tree.
The teenager was pronounced dead after the emergency services arrived on the scene.
A risk assessment carried out by the children’s home had specified that Callum should not be allowed to climb “trees, fences or other obstacles” because he had “little or no” regard for his personal safety.
Mark Peel, chair of the Leeds Safeguarding Children Partnership, said the care worker’s actions “fell short of what should have been reasonably expected”.
The report says not initiating an emergency response straight away was a “major failure”.
It also says that Callum appeared happy on the day of his visit to the park, with no indication he might take his own life.
The care worker has explained his response by saying he went into shock after finding Callum and was “not thinking clearly”.
In a statement, the council said: “We accept all the findings in the serious case review and have already taken action to implement the recommendations made.”