Philip Johnston, 33, has gone on trial at Teesside Crown Court in Middlesbrough.
He is charged with four counts of sexual activity with a child by a person in a position of trust.
Johnston pleaded not guilty to all four offences, which are alleged to have taken place on Teesside.
On Monday afternoon, a jury of 12 people was sworn in to try the case.
The court clerk told them: “The defendant is charged with four counts of sexual activity with a child by a person in a position of trust.
“The defendant has pleaded not guilty and it’s your duty to say, having heard the evidence, whether he’s guilty or not.”
The judge, Recorder Jeremy Baker-Hill, told the jury that the trial is expected to last the rest of the week.
He said: “You have now each affirmed to try the case on the evidence and that’s what you’re going to be doing over the next few days.
“You and I are the judges of this case. You are the judges of the facts and the evidence and I am the judge of the law.”
Recorder Baker-Hill told the jury that they must not discuss the case with anyone else outside of the court.
He also said that all 12 jury members must be present during discussions.
The judge said: “You have a collective responsibility as a jury to ensure not only you comply by these directions but each of you does.
“You’re now judges and as judges we have to try the case without emotional preconceived ideas.”
Johnston, of Hunter Terrace, Sunderland, was granted bail and will return to court at 10.30am on Tuesday.
Paul Cleasby, prosecuting, is expected to open the case when they return to court.