A 44-year-old Staples High School teacher was charged Thursday with sexually assaulting a female Staples student that he was tutoring.

Theron Kissinger of Southbury was charged with two counts of second-degree sexual assault in connection with the incident, which police said occurred as he was tutoring the minor off-campus at town facilities on Bayberry Lane late last year.

Kissinger, a math teacher at Staples who has been placed on administrative leave, also is a top-ranked race walker, according to a 2009 posting on the "06880" blog by Dan Woog, a Westport News columnist. Kissinger was "ranked consistently in the national Top 10 at both 20 and 50 kilometers," he wrote at the time.

"We are shocked and disappointed by these allegations," Superintendent of Schools Elliott Landon said in a statement Friday. "We consider such conduct to be a betrayal of our trust on the part of a teacher that cannot, and will not, be tolerated."

School officials "will continue to work closely with the Westport Police Department, as we have throughout the past few days, to determine all the facts related to this matter and to take appropriate action based on that determination," he said.

"Should these charges be substantiated," Landon added, "we will immediately move to terminate the employment of this teacher."

The police investigation into the incident was made public Wednesday, when school officials alerted the parents of Staples students that a teacher had been placed on administrative leave after they learned police were investigating the teacher in a potential criminal case. Officials said at the time they also had notified the state Department of Children and Families about their concerns.

"The safety of our students is the board's first priority, and the arrest of the teacher is shocking," Board of Education Chairman Michael Gordon said in a statement Friday. "Teacher misconduct putting students at risk will not be tolerated.

I have no comment on the specific facts here, because by law investigation of these allegations is the responsibility of the superintendent, and the Board of Education may be required later to decide this matter as a judge," he added. "The board is confident that the superintendent will act expeditiously."

Because of the police investigation, school officials said the teacher was "immediately" placed on administrative leave after the allegations surfaced. They said they fully cooperated with the investigation.

"Safety is our highest priority for our students and staff, and we will take all action necessary to assure that our schools are safe for all members of the school community," school officials said in the emailed announcement to parents.

Bond for Kissinger was set at $50,000 and he is scheduled to appear Jan. 23 at state Superior Court in Norwalk.