Turn On Event Attachments
To get started, go to your Google Calendar page and click on the Settings "gear". From the resulting list, select the Labs option.
A whole long list of calendar labs will appear. Scroll down to Event attachments and check the Enable button.
Don't forget to click the Save button located at the bottom or top of the labs page. You will now be able to add attachments to your calendar events.
How to Attach Documents to Events
Attaching a document to a calendar event is pretty straightforward. Begin by clicking on the Create button in Google Calendar.
Go ahead and fill out all the pertinent details of your event. If you have multiple calendars, make sure to put the event on the correct one. Additionally, use the description section to communicate additional information. If you are using gCal with your students you can (and should) add class announcements and messages in this space. To add attachments click the Add Attachment link (go figure).
Ok, this part is the only tricky aspect. ALL event attachments have to be in your Google Drive account. If you are attaching a document that is already in gDrive, this is pretty easy... just browse to the file. Otherwise, you can upload your documents to gDrive and attach them to your calendar event all in one motion. There is a critical catch here... the viewer of the event documents must have the correct view permissions on the document otherwise they won't be able to open them. I solve this issue by having a folder in my gDrive called "To Share with Students". This folder is a public folder so I know that anything inside of this folder is viewable to everyone (crisis averted).
Once you have the documents you want attached they will show up on your event. You can view them or click the X to delete them. You can also add additional at this point if you want. Please notice the permissions warning... make sure your guests have the proper permissions to open and view your attachments.
Now anyone who has permissions to view your calendar will see the event. To view the description and attachments they will need to click on the event and select the More details link.
That's pretty much it! It might take you a few attempts before you begin to realize how powerful this functionality can be.
I personally think that adding attachments directly to calendar events can be an elegant time saver and can replace email or even an LMS as the primary mechanism to communicate with students. Try it out.