Barbara,
Performance can be used as a DV but make sure to define what you mean (how you are measuring) performance and have it in the RQ. For example, is it academic performance (GPA) or some other type of performance? And how would you link deviance to performance (is there a cut-off?). You have options but just make sure to specify exactly how you are using the term and how you will measure it and if it is different between your groups (if you use groups). It seems like you might have too many variables in one RQ.
Note what you have in your RQ:
What are the economic and social impacts (how?) that ADHD has on schools, families, the workforce, and the health system?
Variables
-economic impact (need measurement)
-social impact (need measurement)
Across four sample populations (IV): school, family, workforce, health system (note these groups would not be easy to compare to each other on the same DV)
See if you can fine-tune your RQ a bit to zoom in on one IV (can be groups or continuous) and one measurable DV.