Too often, teachers assume that because students spend inordinate amounts of time looking at a screen, they know how to work with technology. Teachers assume that students have it all figured out, that if given an assignment involving technology, students will figure it out or already know how to do whatever they have been assigned.
In many cases, this is true, but I find more and more that most students know some very basic apps, and beyond that, they are as lost as most teachers.
The best way to know what skills students are capable of using is to ask them. Find out what they can do. Find out what apps they know how to use. Find out what devices they are comfortable with.
Students can only be taught what they need to know when the teachers knows what the student needs to be taught.