"Communication apprehension" is a broad-based fear or anxiety associated with either real or anticipated communication with another person or persons. The purpose of this paper, the fifth in a series of five dealing with communication reticence is to speculate on the causes, correlates, and effects of communication apprehension. The effects of communication apprehension in the classroom are especially relevant to those involved in speech instruction. The impact of this problem on standardized achievement tests, grade point average, achievement in small classes, personalized instruction and lecture classes is discussed. Possible causes for communication apprehension, such as intelligence, teacher expectation, student attitudes, and student withdrawal, are also analyzed. (KS)