This paper is based on the premise that an evaluation of teacher performance should consist of an evaluation of the teacher's presentation of subject matter and of the teacher's interaction with the students. In order to develop a balanced evaluation methodology, four English as a Second Language (ESL) classes in two schools on the island of Puerto Rico were observed and taped. Three of the classes were composed of adult students while the fourth class consisted of ten bilingual children, ages 6-7. Presentation of ESL material was evaluated by a comparison of the methodology suggested by three prominent contemporary writers on ESL teaching in the U.S.. The methodologies recommended by these three experts were summarized and the teachers were rated according to which techniques they used frequently. Class interaction was evaluated in terms of a system developed by Gertrude Moskowits who suggested that a language lesson be divided into time intervals of three seconds each. Each interval was then to be coded in terms of ten behavioral categories analyzing the interaction between teacher and students in a classroom milieu. Findings indicated that none of the teachers used the total methodology suggested by any one specialist, but that certain of their recommended techniques were used by each teacher. The teacher who ranked highest in effectiveness used the discovery method. One of the findings of the class interaction analysis was that all of the teachers used more indirect influence than direct in manipulating the class. An observer's ranking of teacher effectiveness is also presented. Criteria for this ranking included teacher poise and personality, class dynamics, and the teacher's use of vocal qualities. (Author/AM)