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 suspect was a 16-year-old boy who had been in and out of the district "a couple of times."
Police Chief Gary Swindle said that Henry was stabbed at least twice in the neck and chest area, reports CBS affiliate KYTX.
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.
Students at the high school, which had been locked down, had been dismissed, a statement Wednesday afternoon on the Tyler school district's Web site said. Classes will resume Thursday.
The stabbing stunned the tight-knit community of 110,000, located about 90 miles southeast of Dallas.
"It's quite a shock," said Tyler Communications Director Susan Guthrie, who received a text message from the police chief soon after the stabbing. "Everybody was very shocked and saddened by the news."
Tyler Mayor Barbara Bass interrupted the morning City Council meeting to observe a moment of silence, Guthrie said.
Jan Henry, the teacher's wife of 10 months, said that when school officials called her to say he was being rushed to the hospital, she did not realize how serious it was.
It was not the first time he had been injured by a student, she said. He missed the first two weeks of school because he was recovering from surgery on a shoulder injured when he broke up a fight at school last year, Jan 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."'
Henry, a native of Chicago, grew up in Huntsville, Texas, after his family moved there in 1973. He was a confirmed bachelor until he married Jan, also an educator.
Henry earned a degree in psychology with an emphasis in music therapy, working for at least a decade as a music therapist, mainly with inmates in the state's prison system, his wife said.
He was self-taught on several string instruments, played in several bands on the weekends and did some studio work.
"He was an accomplished, well-known and respected guitarist," Jody Henry said. "He could play anything."
On his Web site, Todd Henry gave an inkling of how powerful he believed music to be. "I know that music can be a direct link to feelings and passions and is therefore a powerful tool," he wrote.