Misunderstanding refers to an erroneous interpretation of the meaning of an utterance – a failure to understand. The instructional context relies almost exclusively on oral communication. The instructional message can be hampered, no less by the teacher as prime interlocutor whose utterances may result in misunderstandings. To answer the question: "To what extent are misunderstandings the result of English second language speakers' oral proficiency?" misunderstandings were identified in the instructional settings of 26 pre-service teachers who used English as the medium of instruction. This qualitative research drew from ethnographic and case study designs. Speech Act Theory and theories on misunderstandings and instructional communication underpinned the study. Data collection was based on video recordings of the student teachers’ authentic lesson presentations during their internship. Misunderstandings were identified and described in terms of their occurrence, nature, frequency and consequence, e.g. whether they were the result of grammatical clumsiness, cross-cultural transfer problems, or lean vocabulary. These students were not mother tongue speakers of English and the International English Language Testing Score was used to rate their oral proficiency in this language. Focus group interviews were conducted with the student teachers to gauge their awareness of and response to the occurrence of misunderstandings. They also completed a questionnaire in order to establish their awareness of misunderstandings. This small-scale survey also served to provide clarification of information gathered from the interviews. Several iterations of data combing were executed and coding and categorising were done concurrently within each data set. Findings corroborated the initial proposition that misunderstandings in the instructional context occur as a result of poor oral proficiency and inadequate speech act realization patterns. Underdeveloped communication skills included verbosity, unclear enunciation, non-standard pronunciation and inadequate rate of speech. However, what had not been anticipated was that the oral proficiency and speech act realization patterns of the student teachers were considerably weaker than had been expected. Furthermore, methodological factors and inadequate instructional skills similarly compounded the classroom communication. Participants displayed difficulty in formulating effective questions, explaining new concepts, giving instructions and designing well-structured lessons. Their inadequate content knowledge caused erroneous explanations, and poorly structured delivery resulted in instructional dissonance. The overarching theme of failure emerged, namely, inadequate pragmatic competence, underdeveloped content knowledge and scant methodological skills. Recommendations for policy and practice serve to highlight the importance of teachers’ proficiency in the medium of instruction. Coupled with a sound knowledge of the subject field and the prerequisite of well-developed methodological skills, the student teacher will be equipped to teach effectively. Several research topics relating to classroom communication, such as pre-service teacher development courses and cross-cultural and cross-linguistic competence, have been suggested for further exploration.