Of course, you must follow your supervisor's lead,as she will be marking the finished product.
So, the easiest investigation to conduct is a survey.
This would require you to devise a questionnaire
of,say, 20 questions, regarding your area of work.
This can then be handed to a number of colleagues,
teachers, parents and older pupils for completion.
The questionnaire should have a page or two for
personal details, eg. age-range, gender, occupation,
parent or not, years of experience, qualifications,
marital status etc. These details will provide all
the variables you need.
I suggest you use a Likert Scale to record the
responses, from Strongly Agree to Strongly Disagree.
Also give plenty of space for 'Any Other Comments?'
These comments can go into the dissertation
verbatim, with no editing.
Lastly, I strongly urge you to look carefully at
some 'back-numbers' of dissertations which were
successful. Your college library will probably have
hundreds that you can browse. From these, find
a methodology and style which suits you.
Think it over. Meanwhile I'll stick around.