For about the last decade, education reformers have stressed the role of teachers in translating policy reforms into classroom practice. In Lebanon, the 1997 revised English curriculum, which follows learner-centred teaching, has as one of its objectives to enable learners to communicate effectively in English. To meet such an objective, the reformers called for the use of cooperative learning (CL) as it maximises the learners' exposure to meaningful input and output in a democratic, cooperative environment. However, to date a lot of the graduates from Lebanese Public High Schools (LPHS), unlike their counterparts in the private sector, are not proficient enough in English to produce one complete sentence in that foreign language. The aim of this study was therefore to investigate the extent to which the conceptions of teaching that LPHS teachers of English as a foreign language (EFL) have, in general, as well as of CL in particular, are congruent with the curricular reforms and hence implemented into their classroom practice, and thereby investigating one possible reason for their graduates' low proficiency in English. Using a case study design, the researcher examined six Lebanese EFL teachers, purposively sampled, in four LPHS in one city in South Lebanon. Data, collected through observation, interviews, document analysis, and a researcher diary, were compared to ensure credibility. These data, which were analysed thematically, yielded the categories and sub-categories which constitute the results of this research. Major findings showed that (a) there were incongruities between teachers' reported conceptions and their practice; while their reported conceptions lie within learner-centred teaching, their practice, influenced by their learning experiences as language learners as well as their school culture and professional context, was more traditional and teacher-centred, (b) CL was almost absent in their practice, and in only a few occasions were group or pair work activities employed, (c) their teacher preparation was mostly theoretical and traditional, (d) the minimal support provided to EFL teachers in their professional context and the incompatible school culture with the curricular reforms reflected negatively on their practice. Conclusions were drawn as follows: (1) teachers' conceptions of teaching were mostly incongruent with the curricular reforms, and hence these reforms were not translated into the teachers' classroom practice properly, (2) the strong influence of the participants' images of their memorable teachers as language learners, coupled with the participants' inadequate understanding of learner-centred teaching, made the participants equate their friendly attitudes to students with learner-centred teaching, (3) the absence of communication and collaboration between teacher education programme, curriculum designers, and LPHS led to inadequate teacher training, (4) their poor teacher preparation and the inappropriate school culture and context in terms of the physical environment, orientation, and preparedness reinforced the teachers' more established conceptions of what constitute good teaching and discouraged the participants' few attempts to implement traces of these curricular reforms in their classes, and (5) the poor implementation of curricular reforms and the reliance on more traditional teaching, which focuses on form, accuracy, and memorisation, were hence one possible factor responsible for LPHS graduates' low proficiency. The researcher suggested necessary pedagogical implications that are likely to improve the implementation of curricular reforms in LPHS, the most important of which were (a) adjusting the reforms to be in harmony with LPHS professional context as well as culture, (b) more coordination and communication between teacher training programmes, schools, and curriculum designers, and (c) revising the teacher education programme and upgrading teachers' qualifications. Finally, the thesis ends with recommendations for further research.