Collection select default value

Bit of a conundrum, I'm trying to offer a user the opportunity to update 3 drop down collection selects at once which is working fine my only problem is I can't seem to get the default value to display, I've tried using :selected but that doesn't seem to be working, my code looks like:

In the view:

<%@quals=Qual.find(:all)%>

<%for assigned in @degree.assigneds%> <p><label for="assigned_grade">Grade</label><br/>   <%=text_field 'assigned'+assigned.id.to_s, 'grade',"value" =>assigned.grade %></p>

   <p><label for="'assigned'+assigned.id.to_s">Qualification ID</

<br/>

<%=collection_select('assigned'+assigned.id.to_s, :qual_id, @quals,:id, :screen_qual,{},:selected=>assigned.qual_id)%><br /> <%end%>

In the controller

@degree.attributes = params[:degree]          @degree.assigneds.each { |assigned| assigned.attributes = params['assigned'+assigned.id.to_s] }          if @degree.valid? && @degree.assigneds.all?(&:valid?)            @degree.save!            @degree.assigneds.each(&:save!)            redirect_to :action => 'show', :id => @degree          else            render :action => 'edit'         end

if I change the first variable in the collection select from 'assigned'+assigned.id.to_s to just :assigned then it does work but then I can;t work out how to differentiate between the input from each of the drop downs in the controller.

Any help would be much appreciated

still having absolutely no luck with this, anyone got any idea?