A study analyzed quantitatively the effectiveness of public communication as practiced by college students in an introductory speech course. The aim of the study was to test empirically the principles of rhetorical theory on which the teaching of beginning public speaking is commonly based. The study investigated the relationship of mode of delivery--extemporaneous and manuscript--to effectiveness in public communication. Twenty-four samples of extemporaneous and manuscript taped speeches given by undergraduate students were analyzed by students in a communication theory course. Results indicated a significant relationship between the mode of delivery chosen by the speaker and the criteria on which the speech was evaluated. Credibility of the speaker, adaptation to the audience, the use of delivery techniques, and total effectiveness of the communication had a greater significant relationship to the mode of delivery than to organization of ideas and development of ideas. Results also showed a significant relationship between the mode of delivery chosen by the speaker and the positive effectiveness of his/her communication. Most of the speeches ranked superior in every criterion were delivered in the extemporaneous mode. Results seem to indicate that if a student speaker chooses the extemporaneous mode, he/she has a better chance of becoming a successful speaker. (Seven tables of data are included; 16 references are attached.) (Author/PRA)