Reports of internal exam results

I now know that I am missing something obvious! Please tell me how to design a report that lists students with exam results so that I can vary it to present by subject, by year, in ranked order etc...

Depends where you're storing them.
I'd have thought you just start a report based on student then go down to either assessment or exams sub tables and pull out the data.
You can also probably set up marksheets to display the data and export from there which might be easier.

We have set up aspects for each subject (e.g. English mark, Science mark) and result sets for each reporting session (monthly for all students and weekly for some). I am trying to design, in advance, a series of reports to allow us to present results (for internal review) along the lines of:

1. September test results in [subject] for year group, alphabetical and in rank order
2. September test results in [subject] by class, alphabetical and in rank order
3. September test results in all subjects for year group, alphabetical and in rank order

I am spending a bit of time trying to filter the report and it looks like I will have to create multiple variations of it - select result set at run time / select subject at run time / select year group at run time etc. It is also running quite slowly due to the number of queries in it.

This is proving difficult to explain internally because the legacy system (Access - based and set up 10+ years ago) had a "simple" query that printed all of these reports. This appears to compare rather favourably to some staff when the first weekly report print (200 students) took over an hour to process / print.

Is there a more straightforward way to do this?

You could use marksheets to collate the data and then use it live or export to Excel. This could also require multiple versions or filters.
You could also use Independent Reports to pull through assessment data into Word, and make it pretty, but this is more for individual student view.
I have a number of data reports like you've tried, but they tend to have few filters, like, year group and subject. or aspect name contains and they put in comment. stuff like that. It is long winded, but works for certain cases.