The school received an accountability rating of "met standard".
Nearby Stafford Elementary School is also on lockdown. The dropout rate was 1.1%.
Ellis County Commissioner Paul D. Perry said on social media that an unidentified 15-year-old female student was shot and wounded.
"This is a trying time for our community and our school", Joffre said.
The incident took place at Italy High School, 45 miles south of Dallas in Ellis County.
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Other students were prevented from immediately leaving the campus after the shooting, partly in keeping with active shooter drills the school had conducted in the past, Joffre said.
A 15-year-old girl is injured after she was shot at her Texas high school on Monday, officials say. Authorities have said the girl was airlifted to a Dallas hospital. His or her condition is unknown. He said it was also working to make sure grief counselling was available for students.
An Italy ISD parent showed WFAA a text message alert from Superintendent Lee Joffre. He would not say whether the boy has had disciplinary issues at the school. "The suspect is in custody and no longer a threat". Unconfirmed reports on United States media said one person had been injured and was being transferred to hospital.
Italy, which promotes itself as "The Biggest Little Town In Texas", has about 2,000 residents and is located just off Interstate 35 between Dallas and Waco.
No injuries have been confirmed in the shooting.