The police said, an officer, who testified in this North Texas trial, DFW area more or less, suburbs, said, to my surprise, he said it was NOT illegal to have a knife, under a certain length on school property.  Obviously length matters, longer being more potentially harmful, a sword is longer than a knife.  

So generally speaking, for one he was a kid at the time of the offense, the law for certain substances, alcohol, marijuana, cigarettes, guns, controlled substances in general, etc, are different for minors and adults, generally speaking, the law should be clear, small details matter

Possessing any type of knife on school property is strictly prohibited by school district policies across the United States. While state and local laws specify what constitutes a legal or illegal knife, bringing any blade—including small pocket knives and utility tools—onto a campus can result in severe legal and disciplinary consequences. [1, 2, 3, 4]

School Disciplinary Consequences

Even if a knife is legal under state law (e.g., a standard pocket knife), having it on school grounds violates almost all school rules and student codes of conduct. [1, 2]

• Zero-Tolerance Policies: Many schools have strict rules that treat any knife as a weapon.