引用一个变量但第二个指令的两个指令不会触发更改

I have two directives that reference the same parent variable. The first directive is a dropdown. The second directive is a table. What I'm trying to accomplish is this: when a selection is made on the dropdown, the parent variable will change. The second directive using $scope.$watch will detect this change and load the data to the table. Problem is that the second directive is not detecting the change. I'm not understanding why. I have two directives that reference the same p