As a teacher I can say that it isn't always easy to tell, especially if they look and dress like a boy. It's a mistake I've made before and will definitely make again. Not too sure why everyone is calling her an idiot or a bitch. Everyone has made that mistake. Not sure why everyone on here acts like they are perfect. Assholes

that kid will never forget that moment

For all the people asking why OP couldn't tell, you have to realize how many trans gendered kids there are out there. Even in highschool, I see people where I honestly can't tell what gender they are. That being said, I do think OP should have realized a middle schooler would be smart enough to go into the right bathroom and just not said anything

Middle school students need to line up to use the bathroom...?

This is the problem with sex segregated bathrooms. Not only does it make it incredibly difficult for trans+ individuals, but it also causes major confusion when someone who doesn't look like the stereotype of their sex tries to go.

She knows what gender she is/identifies with. Who has bathroom lines in middle school?

I get mistaken for a woman all the time (i have hair that goes lower than my shoulder blades)

Dude what the ****

That's so harsh... Yiiiiikes.