Ricardo Aldana has coached and taught in San Juan Capistrano for the last six years.
Aldana, 37, is accused of sexually assaulting a 14-year-old girl, a former student in his Spanish class at JSerra Catholic High School in San Juan Capistrano.
"He's one of the last teachers I would expect to have something like this happen to him," said student Andrew Irwin. "I thought that it was kind of unbelievable because he was such a nice man."
Authorities say the alleged acts happened in September at Aldana's home.
"As far as investigators know the acts did occur at his home in the city of Dana Point. How he got her to go to his home is still under investigation," said Orange County Sheriff's Spokesman Jim Amormino.
Amormino says Aldana has taught at JSerra for several years. He also coaches varsity boys soccer and junior-varsity girls volleyball.
In a statement, JSerra officials said: "We are outraged and sickened by these disturbing allegations, and are cooperating fully with the Orange County Sheriff's Department."
The statement goes on to say after learning about the facts surrounding the arrest, the school immediately terminated him.
Aldana also coached girls at Tstreet Volleyball Club in Irvine. The club's website says "Over the years, many Tstreet girls have been fortunate to have Ric in their corner as a coach and mentor."
Staff at Tstreet say they just learned of Aldana's arrest Thursday morning. They say in the three years he worked with the club they had no complaints involving him.
"Because of his tenure at the high school, which is seven years, and his association with the various sports clubs, some involving young girls, investigators fear there may be additional victims," said Amormino.
Investigators and school officials hope anyone with information about Aldana will contact authorities.
At the same time, those who know Aldana try to come to grips with the accusations.
"I'm just completely shocked because he's such a nice guy. He's been there for me. Any time I have problems, I could just ask him and he'll be there," said student Christian Trimino.
Aldana posted $100,000 bail and was released.
If you have information related to the case, contact Orange County Crime Stoppers at (855) TIP-OCCS.