The Supreme Court has rejected claims that a teenager in detention was entitled to be considered for enhanced one third remission of his sentence on the same basis as adult prisoners.
The five-judge court said it could not accept that the penal regime that applies to all children should be compared with that established for adults.
The teenager pleaded guilty in 2017 to one count of robbery. He was sentenced to three years detention with 20 months suspended in Oberstown Children's Detention Centre.
After a High Court judgment in other proceedings, which found he was entitled to ordinary remission taking a quarter off his total sentence, his detention was due to expire in May 2018.
Those proceedings concerned an "unjustified distinction" between two categories of young offenders.
In early 2018, his solicitor sought to have him considered for enhanced remission, which would have resulted in an earlier release date.
He later took judicial review proceedings, but his case was rejected by the High Court.
The Supreme Court agreed to hear an appeal because the case could affect a number of others.
In a judgment today, Ms Justice Iseult O'Malley said the core claim was that he had not been treated the same as adults who, he claimed, are objectively in the same situation as him in that they are undergoing custodial sentences.
This claim was "not well founded" and could be successfully maintained only if the rationale of the Children Act 2001, which distinguishes clearly between children and adults, were to be challenged and undermined.
Children are still in the process of development and the policy of the legislature and courts was to assist in that process in a positive way where practicable, she said.
This appellant had not provided any factual basis upon which the court could compare the regime to which he is subject in Oberstown with that applicable to adults.
It had not been argued the system of incremental incentives and planned release under the Oberstown regime was not more suitable for the reality of dealing with young persons than the system of long term incentives available to adults.
While it was true release from Oberstown into the community, under the terms of the Children Act, does not fully equate with the unconditional liberty of a person whose sentence has expired, that should be seen as part of the process leading to the ultimate objective of reintegration into the community.
The court could not accept the penal regime that applies to all children should be compared with that established for adults, she said.
A case such as this raised the issue of "underinclusivilty" as the appellant wished to get a benefit available on a statutory basis only to a category of persons to whom he does not belong. He was essentially seeking an order to be included in a statutory scheme which by its terms excludes him.
That raised issues concerning the separation of powers which, while not necessarily fatal to this claim, had "simply not been addressed in these proceedings".
On foot of those and other findings, the appeal was dismissed.