Well I am not exactly sure pivot table in access the best approach cos of limitations.....but in Access there is no "CountIf" function like excel. So instead, you might want to try:
=Sum(Iif([YourField]=No,1,0))
or =count(Iif([field]=value))
So as for your eg:
=Count(IIF([RankingScore]<=[TargetScore])
Good Luck!