Social media/gaming during lesson time is a big issue at our school.  Presenting this to students as an Challenge/Design brief would be an interesting task. It would allow students to use their knowlege of common distracting apps and come up with a way of limiting/blocking their use during school hours.  It would allow them to work through  Define, Decompose, Functional reqs, contraints process. It could then lead on to research about current apps that do this and identify a niche that may not be served.