Also consider the connection your learner is using.
Many mobile devices only have access to low bandwidth services.
Your learner might only have a 19.2K access, also referred to as dial-up access.
This is what most people had back in the mid 1990's.
Some mobile users might get 56K access and others can assess WiFi broadband.
Since access speeds vary tremendously, make sure your applications do not require high bandwidth and that you are not streaming content.
Make sure all pictures are small and low resolution, so they can be viewed within a small screen and so they download fast.