A Fatal Accident Inquiry in Motherwell heard that Dawn McKenzie was too vulnerable to be trusted with the potential problems of looking after the teenager, who had severe behavioural problems.

Glasgow City Council announced that a probe will be launched into the death, which could lead to an overhaul of fostering services in Scotland.

Dawn, 34 , was stabbed by the teenager she and her husband Bryan were looking after at their home in Hamilton in June 2011.

The boy – Child D – was detained for seven years in 2012 after admitting culpable homicide on the grounds of diminished responsibility. A court heard he suffered a mental disorder at the time of Dawn’s killing.

He appeared to snap after Dawn confiscated his laptop, in agreement with social workers, when Child D used social media to contact his birth mother, with whom his life was “chaotic”.

In his written deliberation yesterday, Sheriff Bicket ruled that the death of Dawn could have been avoided.

He accepted the scathing Significant Case Review of senior social worker Kirsty Maclean, which said the boy was too risky to enter the home of Dawn and husband Bryan, a joiner.

Sheriff Bicket said Dawn’s death might have been avoided had independent agency Foster Care Associates Scotland (FCAS) had “taken proper account” of the couple’s lack of experience as foster carers.

He said: “I am prepared on the balance of probabilities to accept Ms Maclean’s evidence that they should not have been recommended as suitable prospective carers for the child.

“This is not a question of professional negligence, it is a matter of a proper exercise of professional judgement taking full account of the facts which ought to be available and the full circumstances of the case.

“It does seem to me to be a reasonable precaution to have taken proper account of the McKenzies’ status as new carers, their lack of suitable previous experience with children of the age of the said child and the other factors enumerated by Ms Maclean.”

Ms Maclean earlier told the FAI: “I don’t think the placement should have been made and if it hadn’t been made she wouldn’t have died.

“Having a 12-year-old placed brought a number of risks that wouldn’t have been present in younger children.

“I would not have wanted to see them approved for that age range. The likelihood of emotional behaviour problems is heightened with age.”

The sheriff endorsed a range of recommendations in the earlier Serious Case Review, including those aimed at ensuring proper Crisis Prevention and Intervention training for foster parents and careful consideration of potential risks in matching children with foster homes.

A spokesman for the Glasgow City Council said: “This has been an incredibly distressing case and our thoughts remain with Mrs McKenzie’s family.

“A report that will consider the implications of the sheriff’s findings for the council and what action we require to take as a result will be submitted to our children and families committee as soon as is reasonably possible.”

Estella Abraham, chief executive officer of FCA Scotland, said yesterday: “We will now reflect on the full findings and the recommendations made in the judgement to ensure that the foster care provided in Scotland continues to be the best it can be for the children involved and the families who care for them.”

She added: “Dawn McKenzie was highly regarded as a child care worker before becoming a foster carer with FCA Scotland.

“Sheriff Bickett has recognised that in a short space of time she made a positive contribution to a young person’s life. Today our thoughts are with Dawn’s family and Bryan in particular and we wish to express our sincere condolences to them.

“The conclusion of the inquiry was that Dawn’s death was the result of an entirely unpredictable event.”

Members of Dawn’s family were not prepared to comment.