A psychologist asks people to recall the name of their kindergarten teacher. Surprisingly, the majority of people correctly do this and comment, "Gee whiz, I haven't thought about that old bat [or old coot] in years!" Their ability to do so is a severe problem for which theory of forgetting?

There ability to do so is a severe problem for Decay or disuse Theory

Explanation:

The Decay theory is a theory that proposes that memory fades due to the mere passage of time. Information is therefore less available for later retrieval as time passes and memory, as well as memory strength, wears away.  

It proposes that memory not used decay as a function of time.

Hence the situation in the question represents the Decay theory  

Decay or disuse

Explanation:

A psychologist asks people to recall the name of their kindergarten teacher. Surprisingly, the majority of people correctly do this and comment, "Gee whiz, I haven't thought about that old bat [or old coot] in years!" Their ability to do so is a severe problem for which theory of forgetting Decay or disuse

answer; debriefing;