What happens next?

How to tell your teacher you're having your period
Request to use the restroom.
Try to wait until there is a break in the class discussion or a transition between activities. Raise your hand or approach the teacher's desk and ask to visit the restroom.

Choose from: --You can also approach the teacher as a means to request to use the restroom. You may say, " can i use the restroom? " or " excuse me.. --Do this as soon as you suspect that your period is starting so you can avoid any staining. You may need to indicate that you can't wait, as some schools limit bathroom breaks.. --Push your hand back as soon as you pass by and say, " i need to go into the bathroom. Can you excuse me for a few minutes? " or simply ask to use the restroom elsewhere in the room.. --Upon completing this request, go toward the bathroom and pick up your things to go. Write down what you're going to do with your bathroom after class..
Do this as soon as you suspect that your period is starting so you can avoid any staining. You may need to indicate that you can't wait, as some schools limit bathroom breaks.