In a letter to parents, officials said Walnut Bend Elementary School was placed on "hold" at 8:48 a.m. due to the threat before the all-clear was given.
"As a precaution, students and staff are asked to remain in their classrooms in order to keep the hallways empty. Classroom learning will continue throughout the Hold, but students will not be able to change classes," the school said in the letter, adding that HISD police were on site conducting a "systematic sweep" while the campus remained on hold.
School officials said they would continue to monitor the situation.