Responsive design in Storyline 360

Then Rise actually might be the solution, or Storyline with very basic content on the slide. You can preview live how the content will look on different devices to check, as you build.
the only option then is to strip down the content, so instead of trying to but one Slide of content on the screen, split it out to several slides instead. If 70% of the students are using their Smart Phones, then unfortunately based on Needs Analysis, you will have to build to meet the need. My only criticism is that, if you have recommended that the users use a laptop or Tablet and they are ignoring your instruction, then they should not be in a position to be complaining. It seems to me that the students are trying to inconvenience themselves to attempt the course so make their lives easier, instead of making a concerted effort to sit down and actually take part in the course. Its tough love :)