Some of the responses so far seem to be based on the assumption that this is an information technology class for students who intend to specialize in the field. I'm assuming, rather, that this is intended to be a basic primer class offered to everyone and intended to give a general grounding in the subject.
My suggestion is that you start by talking to adults to find out what they do and don't understand about the technology they use. In my experience (20-some years' worth of dealing with end users in various capacities) many, probably most, adults have an extremely limited idea how the technology they are using really works in the physical world and deal only with it as an abstract unit. And some of the assumptions they make based on the mental model they have built up lead to really bad decisions because they don't understand very basic concepts that the rest of us take for granted.
To give an example: perhaps the single most misunderstood concept I encounter is the notion of storage. A great number of people seem to have no idea what actually happens on a computer when they save something. Generally they don't understand the difference between various types of memory (i.e. the difference between temporary short-term storage in RAM and long-term storage on a file system on some sort of disc or flash device. They have a very limited understanding, if any, of the filesystem and the concept of hierarchical organization. They are generally unable to distinguish between the various components of their system (e.g. display, CPU, input devices, file storage.) These are things that seem idiotically simple to most of us because we have completely internalized the knowledge, but deal with people who don't have the same underlying framework and you will soon see how it affects their reasoning about their computer.
People with this sort of limited understanding of the computer as one abstracted whole, a magic box that they interact with, generally get along adequately as long as everything is working the way they expect but as soon as they run into any sort of exceptional circumstance they have virtually no recourse because they have no real understanding from which to base hypotheses about a possible cause for the problem or method for proceeding. Their ability to use their systems is therefore fragile and subject to disruption from virtually any sort of unusual situation.
If you've worked in the field you've seen this over and over and over again and you can probably call to mind some of the unfortunate results of this kind of shallow understanding and "magical box" mindset.
I think the best thing you can do for kids just getting started (though I think 9th grade is pretty late to be getting started) is to help them understand that computers are not magical and that their behavior is not arbitrary, that with the proper basic understanding of what's happening most of what follows can be predicted by fairly straightforward logic.