"You're talking about a Star Wars T-shirt, a week before the biggest movie of the year comes out. It has nothing to do with guns or making a stand. It's just a Star Wars shirt."
Texas is famous for having some of the most relaxed gun laws in the US, and in May passed a bill allowing people to carry guns openly on the streets. About 850,000 Texans have a licence to carry a concealed handgun - a number that has increased sharply in recent years.
Yet the school defended their decision to ban the T-shirt.
A spokesperson for Lamar Consolidated Independent School District told the local television station KTRK that the handbook spelled out potential violations of dress code, including "symbols oriented toward violence".
The school administrators said they did not reprimand Colton, although they could have required him to change or suspended him. They say they only required him to zip up his jacket.
But Southern said his son was entirely within his rights to wear the T-shirt, as the weapon shown is fictional - just like the character holding it. He said the implication his son would hurt anyone would be incorrect.
"He's a Boy Scout, active in church, volunteers at Brazos Bend State Park," he said.
"There's not a violent bone in his body. He's just an excited kid for the movie."