The offences occurred on two separate occasions in November, 2012.
The police summary of facts reveals that between October 27 and November 3 Loader communicated with a 19-year-old male on the social networking website, Facebook.
Loader and the male teenager were known to each other, as the 19-year-old was a former Otumoetai College student.
The 16-year-old girl was not a current or former student of the college.
An agreement was reached that Loader would pay $120 to watch the male teenager and the 16-year-old girl, who he had been told was 17, have sexual intercourse.
This occurred twice and Loader paid a total of $240 after withdrawing the cash from an ATM.
Judge Peter Rollo convicted Loader of the charge and remanded him on bail pending sentencing on March 15.
While on bail Loader, is barred from associating with the other parties to the sex services contract.
Outside court Loader declined to comment.
He resigned from the school by mutual agreement and the matter is also being investigated by the New Zealand Teachers' Council.
Otumoetai College principal Dave Randell said when the news first broke he and other teaching staff were shocked.
"Andrew was a popular teacher who worked at the school for nine years and he was also involved in the Young Enterprise programme at the school ...
"There was total dismay among the staff, we just couldn't believe it," he said.
Mr Randell said Loader's "unbecoming conduct" was very disappointing. However, he added, the public could have complete confidence the school had taken the appropriate disciplinary action.