In the 21st century one of the reasons for teachers to pursue continuous professional development is experiencing demanding situations in their lessons, because the concept of mixed-ability teaching has broadened schools being open to diversity. Consequently, different pupils learn together in comprehensive schools and have equal rights to quality education. That also regards language learning. In the present article the authors look upon a situation in which a teacher of English in a comprehensive school has to deal with groups of primary school pupils who have varied needs and preferences for learning a foreign language both academically and socially (for example, having problems with reading and understanding the read material, focusing and keeping attention, working in pairs or groups). Therefore, the use of differentiated activities to enhance primary school pupils’ acquisition of the English language is explored. The chosen research method is a case study in which 14 primary school pupils take part. Data collection methods used in the research are observation (a teacher’s diary to notice the pupils’ strengths and weaknesses of learning English and checklists to gather the evidence of the pupils’ learning achievement) and document analysis (test evaluation forms to record the pupils’ learning results and progress). The analysis of the gathered data shows that the use of the chosen differentiated activities, which are based on the ideas of mixed-ability teaching and inclusive education, has helped the pupils improve the acquisition of the English language The results of the case study allow the authors to conclude that the varied needs and preferences pupils have for learning a foreign language are a compelling reason for teachers to find new ways of teaching to be able to help each learner prosper.