To have these added to your subscription, just follow these steps:
1. Click on your display name in the upper-right corner of the screen.
2. Click "Account".
3. Click the three-dot icon in the upper-right corner and select "Get Free Months".
4. Enter your information to create your school or, if you believe someone at your school already uses Planbook.com, click the "Look For School" button.
5. Click the save/apply button, and you will have a "School ID" on your "Account" page now.
When five teachers have done this, you will receive three months free automatically added to your account. When ten or more teachers do this, you'll receive six months free.