Nowra man Eric Thomas Staggs will remain in jail until November this year for stealing thousands of dollars worth of equipment from St John the Evangelist High School.
Staggs, aged 27, in company with another man and a woman, broke into the high school about 10.30pm on May 17 this year.
The trio took numerous items from the school, including glasses, batteries, 41 thumb drives, lighters and $58.55 in cash.
They set off a security alarm, and were arrested shortly before 11.20pm. Police facts say Staggs and the woman claimed the third man had threatened them, and they were forced to commit the robbery at gunpoint.
Staggs later plead guilty to aggravated break, enter and steal in company.
Magistrate Gabriel Fleming said while the stolen items were unlikely to have sentimental value, the crime was still "appalling".
"Every single child who goes to that school will be affected," she said.
Staggs has an extensive criminal history, however, most of his previous offences are driving offences.
Magistrate Fleming sentenced him to 18 months imprisonment, with a six-month non-parole period, backdated to the time of his arrest.
He will be eligible for release in November.