The recommended method for GCISD mail and calendars on a mobile device is to use the Google apps.
Using Gmail or Google Calendar on your phone or tablet is as simple as downloading the apps. No matter what platform is, either iOS or Android, all you have to do is sign in with your GCISD email address and password. This is also true for all the Google apps such as Drive, Docs, Sheets, Photos, Keep, etc.
Note: Students are not able to download the Gmail or calendar apps on district-owned iPads. They can, however, download the other Google apps such as Drive, Docs, and Sheets.