When joining a class, if a student gets the message "Couldn't find class", then either the PIN they are entering is incorrect, or they cannot access the class from the device they are using. This happens when a student tries to access an iOS class on an Android tablet and vice versa.
Please note that the iOS and Android versions of Handouts are currently NOT compatible. We are working on having this functionality ready as soon as porrible, but in the meantime you cannot access the same class using a mix of Android tablets and iPads - teacher and students must all use the same platform.
If this doesn't seem to be the problem please get in touch at firstname.lastname@example.org, letting us know the account details for you and the student(s) in question, what system they are registered on (iOS/Android) and the PIN code for the class in question. We will look into the problem as soon as possible.