The 17-year-old student spent the weekend with his parents and did not attend the party where the sexual assault allegedly took place, attorney Fernando Valdes said.
The boy was stabbed three times Monday at Wunsche High School and remained hospitalized Tuesday in good condition.
"He was not at any party at all," Valdes said. "This kid was student of the month last month. He's not some thug that runs around gang banging. He hangs around computer guys. He's a techie, a good guy getting a bad rap."
Harris County Sheriff's Sgt. Kenneth O. Thomas said investigators had not yet confirmed whether the boy was at the party.
"This was an unwarranted act of vigilantism," said Valdes, who said the boy knows the girl but had never before seen her father.
The man went to the school Monday with his 17-year-old daughter and wife to report the sexual assault to school administrators.
Valdes said the man spotted the boy in the school lobby, called out to him and lunged at him from behind, stabbing the boy in the chest, one hand and the abdomen.
The teenager knocked the knife out of his attacker's hand before school police subdued the man.
Spring Independent School District police arrested the girl's father and charged him with aggravated assault with a deadly weapon. Court records did not indicate whether he had an attorney to speak for him, and a telephone number listed for his address had been disconnected.
Court records show that the 44-year-old man had received deferred adjudication for discharging a firearm in 2001, and pleaded guilty to theft in 1990.
The girl's parents had reported the sexual assault to Harris County Constable Precinct 4 over the weekend. Sheriff's officials on Monday confirmed they were investigating the incident.
"We don't even know if a sexual assault took place," said Lt. Ruben Diaz of the Harris County sheriff's sex crimes unit. "She doesn't really know what happened."
The Associated Press is not naming the man because his daughter may have been a juvenile victim of sexual assault and could be identified through the father's name.