In the age of information and communication technologies the English language plays a significant role both in oral and written communication. The successful performance of computer programming specialists largely depends on their level of lexical competence, so a university course of English for specific purposes (ESP) focused on its development, can be exceedingly useful in the professional training of prospective programmers. This study aims at investigating the effectiveness of the

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... tive professional written communication in ESP classrooms to enhance future programmers' writing skills as well as improve their English lexical competence. To validate the efficiency of the algorithm, the author conducted experimental teaching of the 5th-year students of the Faculty of Applied Mathematics and Informatics at Ivan Franko Lviv National University in 2017‒2018 academic year. The stages of the algorithm implemented in order to advance the level of English lexical competence were elaborated. Efficiency of the algorithm has been proved on the basis of the results obtained from pre- and post- experimental assessment of students from experimental and control groups. On a practical level, the participants' writing skills were examined through an English written test prior to and after cooperative learning activities were provided. Growth rate in students from experimental group significantly exceeded the students' results in the control group. Thus, the efficacy of the suggested algorithm used for developing lexical competence in computer programming students has been proved. In light of the findings, the researcher indicates that teachers can benefit from applying the proposed methodology for collaborative professional writing in English classes, which may in turn develop students' writing skills and improve their English lexical competence.