"The boy - who had cerebral palsy, epilepsy, profound intellectual disability and spastic quadriplegia - was fully dependent for all cares and received respite care at times at a residential facility [the home].
"One overnight shift two support workers were together caring for the boy and five other high-needs young people. The boy was assisted into a bath using a hoist. There were instructions that children should never be left unsupervised whilst they were in the bathroom area and the boy's personal support information also stated that he should not be left alone.
"However, a practice had developed at the home where the boy, and other children, would be left alone in the bath for short periods of time,'' the report said.
"This evening, the boy was left alone in the bath while care was provided to other children, he was later discovered submerged in the bath not breathing. He was taken to hospital but later died."
The Deputy Health and Disability Commissioner, Rose Wall, said in the report that the policies at the home should have been assessed.
Regular refresher training should also have been carried out to minimise the risk of practices moving away from policies over time.
"There is no value in a policy that is not followed by staff,'' she said.
The teenager involved - who had the capabilities of a 6-month-old baby - has not been named in the report.
IDEA Services was prosecuted by Worksafe NZ and was fined a total of $63,500. The organisation was also ordered to pay $90,000 reparation to the teenager's family.
A female carer who put the teenager in the bath that night was initially arrested and charged with his manslaughter just over a year after his death.
However, late last year, there was a decision in the High Court and the charges were dropped. The woman and the second support worker involved, a man, were both granted permanent name suppression.
Since the incident, the home has made changes to its policies.
Wall also made several recommendations to the facility - including putting in place personal and risk management plans specific to each person, so that all staff knew what was required for them in any given situation.
The disability services provider and the two support workers involved in the incident were asked by the commissioner to provide an apology to the teenager's family.