Todd R. Henry, 50, worked with students at John Tyler High School who were either emotionally or behaviorally challenged, according to his older brother, Jody Henry.

"He loved it," the elder Henry said. "He told me it was his calling. He had never been happier than when working with these kids."

District Superintendent Randy Reid said the male suspect approached his teacher about 8:50 a.m. and stabbed him in the neck with a sharp object. A teacher's aide and two other students were in the classroom, and the aide subdued the suspect before calling district police, Reid said.

Reid said the student had been in and out of the district "a couple of times," but declined to provide further details, citing privacy laws.

"It is our understanding at this time that there was nothing in the classroom that incited this situation," Reid said. "It was a random act."

The high school was locked down after the stabbing and students were eventually sent home for the day, according to a statement on the district's Web site. Reid said classes would resume Thursday.

Jan Henry, the teacher's wife of 10 months, said he had been injured by a student before. Todd Henry missed the first two weeks of school recovering from shoulder surgery after he broke up a fight at school last year, his wife said.

"He worked in a prison for 10 years. Do you think this man was afraid? Get real," Jan said in a telephone interview from her Tyler home, surrounded by close friends and family. "We'd be eating out and a student would walk up and shake his hand. He'd look at me and smile and say, 'That's what it's all about.'"

Police did not offer a motive behind the stabbing and referred further questions to Angela Jenkins, a spokeswoman for the high school. Jenkins did not immediately return messages left by The Associated Press.

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Linda Stewart Ball reported from Dallas. Associated Press writers Diana Heidgerd and Schuyler Dixon in Dallas contributed to this report.