You can delete a teacher account by following the steps below:
1) Log in to your teacher account at classroom.freckle.com
2) Click on your name in the top right corner
3) Select "Settings" from the drop down menu
4) Click on "Delete Account" on the bottom right
5) Follow the directions and type in "I AM SURE" into the dialog box
* Note that once you delete your teacher account, you permanently lose student data.