The pair do have some knowledge of the Wellington Centurion side, however.
"We played them this season in a rep game and we got a bit of a hiding," Cameron said.
Both, however, are confident it will be a different ball game with players of national quality at their side on Saturday.
The majority of the 23-man squad should get a run this weekend and Cameron and Monaghan are race fit after helping Cullinane win the Wanganui secondary school competition after an emphatic 39-3 victory over Wanganui City College in the final.
"The problem will be that the Centurions have played together as a unit all season and will be well drilled," they said.
Year 13 student Monaghan, 18, plans to play club rugby next season - probably for Marist - after leaving school, while 17-year-old Year 12 pupil Cameron will have one more season in the Cullinane 1st XV before deciding his future.
Cameron will still be eligible for re-selection into the national Catholic squad next season, leaving Monaghan just this Saturday's game to impress other national or franchise selectors ahead of the 2014 rugby season.
Cullinane principal Kevin Shore said he was proud of the pair and said their selection was a huge achievement.
The formation of the Catholic team was driven by Marist New Zealand.