If the variable is not visible to you while you've added it, then it may be out of scope; it may actually be a local variable. Create it outside the scope, at start of event sheet is best for global variables.
Just guessing.
I didn't think Construct Classic had local variables <img src="smileys/smiley5.gif" border="0" align="middle" />
crow, you can try global('score') to pull it's value in an expression field, and look in the System object for conditions and actions related to global variables.