A study investigating the perceptions of students of English as a second language (ESL) regarding formal and informal speech in English also looked at their implications for teaching ESL. It was proposed that because the manner of speech a teacher uses may influence the students' ability to acquire the material presented, it may be helpful to understand learners' perceptions of one aspect of teacher language, the degrees of formality. In the experiment, 30 intermediate level ESL college students listened to 12 recorded speech samples of one speaker using four degrees of formality/informality as defined by phonological variations in contractions and reduced forms of words. The students then completed a separate test protocol regarding their perceptions of each statement. Resulting mean scores indicated that ESL students perceived the speaker using formal speech as more educated, polite, easy to understand, interesting, and helpful than the speaker using informal speech. Results from a one-way ANOVA indicated a significant difference in ESL students' perceptions of the speaker as being educated and polite when formal speech was used. The results suggest there may be advantages in teachers' using more formal speech in the classroom. (Author/MSE)