The present study was designed to investigate the effectiveness of EFL teachers and, more specifically, to identify the competencies of the effective EFL teachers at the preparatory school level in Oman. To attain this objective, the following research questions were addressed: 1. Are there any significant differences between the "effective" and the "less effective" teachers in terms of their teaching competencies? 2. How much consistency is there in the competency differences between the "effective" and the "less effective" EFL teachers when the specific factors of gender and nationality are considered? 3. Is there a relationship between EFL teachers' competencies (as determined by the researcher's observation) and the background variables such as gender, nationality, qualifications, in-service training and educational regions? 4. What are the most and the least important competencies that are perceived by the educators to characterize the work of effective EFL teachers at the preparatory school level in Oman? 5. To what extent does the educators' perception (about the skills of effective EFL teachers at the preparatory school level in Oman) vary according to their professional background, gender, and nationality? *** 21 6. What are, in qualitative terms, the specific instructional processes (skills and behaviors) that are associated with the work of "effective" and "less effective" EFL teachers (as determined on the basis of the supervisors' classifications)? The sample included was 100 EFL preparatory school teachers. These teachers were observed by the researcher and were later classified into two groups ('effective and 'less effective'), using the Ministry of Education's criteria. Additionally, there were 120 informants (EFL educators) who responded to a questionnaire on what they perceived to be important characteristics of effective EFL teachers. The instruments used were: an observation checklist, a questionnaire, and ethnographic narratives. Both the observation checklist and the questionnaire were validated by a panel of specialists. The inter-rater reliability of the observations was established through the correlation technique which yielded coefficients of about .90. The data of the observation and the questionnaire were subjected to different statistical techniques, namely descriptive statistics, t-test, ANOVA, and correlation. The ethnographic data, on the other hand, was not analyzed statistically and was, instead, examined in qualitative terms. The results of the study showed that: (1) The "effective" and "less effective" teachers (as determined by the classification of the ELT supervisors of the Ministry of Education) exhibited significant differences between them on all the teaching competencies that were considered in our classroom observation. (2) The teaching competencies were strongly inter-related, which suggests an inter dependence and an interaction among them in the teaching process. This interdependence was further confirmed by the qualitative (ethnographic) observation. (3) The differences between the "effective" and the "less effective" teachers remain consistent and stable, across the gender and nationality sub-groups that made up the total sample.. (4) The teaching competencies (as observed by the researcher) were generally not greatly affected by the teachers' background factors. This is especially the case with the qualifications, in-service training, years of teaching experience, and the educational art Vete regions. However, some competencies showed a significant effect for gender (in favor of females) and for nationality (in favor of the Omani teachers). (5) Almost all the 12 categories of competencies considered in our study were perceived by the EFL educators to be important. Only three were below the theoretical mean. These three competencies were not greatly affected by the respondents' backgrounds, which indicates that there is a general consensus on what constitute effective EFL instruction. The recommendations suggested by the study included: (1) Using the competencies considered in this study as a basis for teacher training and teacher evaluation; (2) Giving more importance to classroom research in the training of English teachers in Oman; (3) Conducting a needs analysis in the area of teaching competencies for diagnostic and in-service training purposes; (4) Carrying out similar studies on effective instruction, using different and more experienced observers and more sophisticated techniques.