Questions Help with subreport parameters

I'm creating a master report with multiple subreports.  The master report only contains one table and it has 3 parameters - Start Date, End Date, and Rate.  The parameters need to be included in filters within the subreports but when I view the master report, no data shows up in the subreports. 

The subreports run correctly when executed separately outside of the master report with the same set of parameter values that I am running the master report with.   

I attached screenshots - sorry for not being able to use imgur at work; I hope the attachments work ok.

Master report parameters screenshot:

Subreport parameters screenshot from Schema Builder: (the @Rate text box in groupHeaderSection1 is supposed to be a basic way to see whether the parameters are working - no value shows up)

Any suggestions for what I'm missing would be greatly appreciated.