Value from other dataset returned value

I have a report with two datasets. One dataset gives the values (names) for a dropdown list.  The other dataset takes that name chosen from the dropdown list to create the rest (a graph) of the report. Its that second dataset thats not quite working.  Its not catching the name chosen from the dropdown list. Here is what I have:

declare @name varchar(50)

select ID, Grade
  from tGroups
where ID = substring(@name,1,5)