There is a chance that they are not using devices that meet our minimum requirements. https://help.tenmarks.com/hc/en-us/articles/204938054-Technical-Requirements

If your students are logging in from mobile devices, please ensure that they are using our app instead of a mobile browser (Safari, Chrome). https://itunes.apple.com/app/id672032789 http://www.amazon.com/gp/mas/dl/android?asin=B00KMAB296 https://play.google.com/store/apps/details?id=com.tenmarks.android.ps