Shane Matthews was once described by his students as "the greatest teacher in the school".

But today, Campbelltown Court was packed with former pupils and parents of a former primary school in Sydney's south-west, who were eager to see Matthews jailed for the systematic sexual abuse of more than a dozen children in his care.

A Campbelltown judge found the 31-year-old former teacher guilty of abusing 17 students at Wattle Grove Public School between 2012 and 2015.

Today, he was sentenced to 18 years in jail with a non-parole period of 12 years.

Matthews was found guilty of grooming young boys by offering them fake money and prizes on "superhero" days.

The abuse occurred during lessons, recess, lunchtime - even in scripture class - where Matthews would ask students to perform acts on themselves or perform sexual acts on them.

Victims were "encouraged, enticed and recruited to engage in offending activities", the crown prosecutor said.

Matthews bribed the students with fake classroom currency, even gifting them erasers and pencil cases to ensure his crimes were kept quiet.

He was arrested in September 2016 and initially charged with 14 offences but more were added as victims came forward.

Pleading guilty to 33 separate charges today, Matthews sat shaking uncontrollably in the dock as he was sentenced to a maximum of 18 years in jail.