Maybe there are multiple DNS servers for the zone that are returning different IPs, maybe one or both of them is even in split-zone configuration so it returns a different IP depending on if you're internal or external. Maybe the client has manual DNS configured or a hosts entry that's wrong.
Each of these problems would have several more layers of troubleshooting steps and branching, and it's not even a complete list -- and this is only if the problem is DNS-centric! There's hundreds of other branches for each of the other problem categories.
Of course in reality there can be more, weirder things — especially if you are coming into an unknown network. But we are talking about an educational context here, would not make a lot of sense to let your students run into new unknown issues on a test unless your goal is not to educate.
Often debugging is a hunch, and quickly branches. One person will go down the path of trying the same site from another PC. Another will try a different site from the same browser/PC. Another will try to ping the server.
If you're running this live you're always going to have the chance where someone's hunch or first try basically pinpoints the problem and eliminates a dozen checks from their consideration. If you're looking for things like "did they check DNS? Did they try another site?" but they skipped that and immediately figured out apache wasn't running, do they lose points? Or do they get 100% for their lucky (and/or experienced) guess?
If you do it on paper, the major problem is basically infinite branching for every step and possible result. How do you mark that? What's the minimum you need to do to get 100%? I think it's also unfair, because even as a seasoned vet I've been deep in troubleshooting to the point of (for example) greping source of nginx for a specific error message -- which I'd never have even thought of two steps earlier. I do t expect anything that complex on a school test of course, but the point is the result of each step is often the only way to even think of the next.