Video from SkyEye shows hundreds of people standing in front of and behind the school.
SKYEYE: Students evacuating Aldine's MacArthur HS
Raw video: Students outside MacArthur HS
Students appeared to be walking back into the school around 8:30am, but we have not yet heard whether the situation was all clear.
Administrators said earlier that students and staff were being moved away from the building as a precaution.
The cause of the gas leak was not immediately clear.
Stay with ABC13 Eyewitness News for the latest details on this developing story.