Can you imagine what it'd be like if that was the law? It would mean we'd finally have to create a definitive value of "hotness" and a way to measure it, to make sure the teacher in question was hot enough to sleep with an underage kid. And of course, the entire thing would be debated to hell and back because everyone's idea of hot is different. I can see the courtroom battles now...
"Your honor! The defendant is clearly only 46% hot, and a mere 3.6 on the 'Bow-Chika-Wow-Wow' scale, making her classification 'Pretty,' not nearly hot enough to be screwing around with minors!"
"I object! I find the defendant to be quite hot, sir. In fact, if given the option, I'd tap that ass right now!"
"That's inconsequential! The Hotness Determining Guidelines are quite clear on this. Subject must be blonde, tan, and have breasts of AT LEAST a size double D to score high enough to be able to boink little boys!"
"But red-heads are WAY hotter than blonds! And if the breast is more than a handful, what's the point?"
"ORDER! Order in the court!"