KEEPING a troubled child at one of the state's detention schools cost an average of €540,000 per youngster last year.

The costs rose as high as €614,000 for each of the (on average) five females detained at Oberstown Girls' School last year, figures from the Department of Justice reveal.

Overall, the four centres open in 2009 were operating at just above half of their total capacity throughout the year.

The cost of detaining the youths dwarfs the total bills for offenders in the Irish Prison Service. By comparison, the average annual cost of keeping an offender at high-security Portlaoise prison is €269,800, while in Mountjoy; it comes in at €99,800.

At Oberstown Boys' School, the equivalent of 79.5 members of staff cared for just 12 troubled youths last year.

The average bill per child there – all aged between 14 and 17 – was €451,666 from a total running cost of €5.4m.

At the Oberstown Girls' School, average occupancy at the centre was just five, with 50 staff employed at the centre. The running cost for 2009 was €3.07m and the centre had a capacity of 12 last year.

The Finglas Child and Adolescent Centre was the busiest of all the facilities, operating at two-thirds of its capacity with an average of 12 youths detained there last year.

The cost per offender was €480,416 with the whole-time equivalent of 88.5 staff employed at the €5.7m-a-year centre, which has since been closed.

Lastly, and most expensively, was the centre at Trinity House where an average of just ten youths were detained despite a capacity of 27.

The average annual cost per teenager was €695,000 out of the total cost of €6.95m spent on more than 90 staff as well as general upkeep and administration.

The Department of Justice said the cost of the €21.1m a year service would be cut by the closure of the centre in Finglas. A statement said: "As approved by the Minister for Children and Youth Affairs [Barry Andrews, the] Finglas Centre closed on 31 March 2010, with the transfer of staff and services to Oberstown.

"This will accommodate the government's plans for an integrated campus and new national children detention facilities on the Oberstown site.

"The various staff employed by the Children Detention Schools includes care, catering, building maintenance, nursing and clerical staff. It should also be noted that the schools are staffed on a 24-hour basis."

Other young offenders are also housed at St Patrick's Institution in the Mountjoy complex, which caters for prisoners aged between 16 and 21 years of age.