A teenager who broke into his old primary school and defecated on the secretary's chair has today avoided jail.

Joshua Forrest Duxbury, 19, slipped through an unlocked staff room door at Clinton Primary School in South Otago at about 1.37am on November 29 last year.

He then spent the next three hours wandering around the school complex.

All the while, he was spotted on CCTV.

When he wandered into the principal's office, he took a can of Coke.

Then he rifled through the principal's desk and took about $10 in change.

He also pilfered an unknown amount from a small money box sitting on the desk.

Back in the staff room, he found the fridge and ate the remains of a chocolate cake before taking a lie-down.

He then took a large box of chocolates from the reception area, along with a cellphone and charger.

But Duxbury's lowest moment came when he sat on the secretary's chair and "defecated on the seat and the cushion" and also "several areas of the carpet near the chair".

He was seen leaving the school around 4.30am.

When police caught up with him about 7.15pm that night in Clinton, he was found in possession of the cellphone and an unopened box of chocolates.

He admitted going to the school and telling officers he had been "extremely drunk".

"He could not give an explanation for his actions," a police summary of facts concludes.

Duxbury was charged with burglary and appeared for sentencing at Christchurch District Court today.

Victim impact statements provided to the court said the school's staff and students were left "extremely upset" by the invasion.

Staff were left feeling unsafe, violated and disgusted by the mess left behind.

Defence counsel Olivia Jarvis said Duxbury was remorseful, apologetic, disappointed and "embarrassed at the way he behaved that night".

He'd just been released from prison earlier that day and gone from "no liberty to all the liberty" and "taken to alcohol in the extreme amount".

After the death of his father in May last year, Duxbury's life took a dramatic turn for the worse, Jarvis said.

He's now moved to Christchurch and is turning his life around. He's stopped drinking and is looking for work.

Judge Raoul Neave said there was little doubt that his life "came apart in a major way" following the death of his father.

He sentenced Duxbury to 18 months' intensive supervision with special conditions to counselling, grief support and general life skills.

Duxbury must also complete 200 hours of community work, be subject to judicial monitoring, and make reparations of $540.51 at a rate of $5 a week, which can be increased once he gets a job.