The Castro Valley Unified School District put a teacher on paid administrative leave Friday after receiving "allegations of an inappropriate relationship" between the teacher and a high school student.
District Superintendent Jim Negri would not say whether the complaint was sexual in nature or whether it was made by a student or a parent.
Nor did he reveal anything about the names or genders of the teacher and student involved.
"We have to handle this in a way that protects everyone's privacy," Negri said.
Negri said district officials want to get to the bottom of the allegations soon without compromising everyone's right to due process.
"Ideally we'll get it resolved as quickly as possible, but I've seen these things drag on for six months," he said.
Law enforcement has been notified. Negri said sometimes legal authorities conduct a parallel investigation, other times not.
No matter what school or law enforcement officials do or don't do, Negri said nothing will be disclosed unless and until a criminal charge is filed — and at this point it would be premature to speculate about any such thing.
The district has not yet notified parents but is considering such a notification, he said.
Complaints about misconduct of this type at the school are very rare, Negri said.