Young people aged 16 and 17 are supposed to be placed in secure accommodation rather than young offender institutions (YOIs) under the Children (Care and Justice) (Scotland) Act, which became law last month.
A 17-year-old boy has died at a young offenders institution - two years after the Scottish government pledged to stop sending under-18s to the facility.
Jonathan Beadle died at Young Offenders Institution Polmont, in the village of Reddingmuirhead near Falkirk, on Saturday.
It is understood the teenager was previously in a secure children’s unit before being moved to Polmont.
Young people aged 16 and 17 are supposed to be placed in secure accommodation rather than young offender institutions (YOIs) under the Children (Care and Justice) (Scotland) Act, which became law last month.
Police Scotland confirmed the death is being treated as "unexplained" but there are "not thought to be any suspicious circumstances".
A report will be submitted to the Procurator Fiscal.
A fatal accident inquiry (FAI) - which is mandatory for all deaths in custody - will later be held to examine the circumstances.
A Scottish Prison Service (SPS) spokesperson said: "Every death, whether in prison custody or in our communities, is a tragedy for all those who knew and supported the individual."
In March 2022, the Scottish government vowed to end the placement of 16 and 17-year-olds in YOIs.
It was part of a plan containing 80 actions to "improve the lives of children, young people and families in and around the edges of care".
Then minister for children Clare Haughey said the move would be made "without delay", with "care-based alternatives" to shift the approach from "one of punishment to one of love and support".
It came after Wendy Sinclair-Gieben, Scotland’s chief inspector of prisons, led calls for no one under the age of 18 to be sent to jail.
At the time, Ms Sinclair-Gieben said the results of a survey of 16 and 17-year-olds at HMP YOI Polmont were "shocking".
The result of a joint FAI into the deaths of two young people who took their own lives at Polmont is expected to be published later this year.
Katie Allan, 21, and William Brown, 16, were found dead in their cells in separate incidents in 2018.
Katie Allan. Pic: PA
Ms Allan, a student at Glasgow University, was found dead on 4 June 2018 while serving a 16-month sentence for drink-driving and causing serious injury by dangerous driving.
William, who was also known as William Lindsay, and had been in care repeatedly, was sent to Polmont because there was no space in a children’s secure unit, having walked into a police station with a knife.
He was found dead on 7 October 2018.
Victims and community safety minister Siobhian Brown said: "Every death in custody is a tragedy and I extend my deepest condolences to Jonathan’s family.
"As a report will be submitted to the Procurator Fiscal, it would be inappropriate to comment further.
"The Children (Care and Justice) (Scotland) Act, which received royal assent on 4 June, includes provisions to end the placement of under-18s in young offenders institutions.
"We are working with the Scottish Prison Service and secure accommodation providers to commence these provisions shortly.
"The decision on whether to detain a child remains with the independent judiciary."