This study investigates what can cause significant gaps in grammatical knowledge in a class of English 5 and how such gaps can be healed or avoided. By triangulating results from two diagnostic tests, a focus group of pupils and a semi-structured interview with their teacher, data were analysed statistically and through a phenomenographic perspective.  The results expose grammatical gaps concerning genitive construction, relative pronouns, and tag construction. Moreover, the pupils’ experiences from earlier grammar teaching and learning indicate that cause, development, and possible healing of grammatical gaps are related to how grammar seldom is discussed or practised in school. Furthermore, the teacher’s experiences show how pupils and groups typically unaffected by grammatical issues now are involved and that extensive repair efforts are needed. In conclusion, the results and analysis suggest that grammatical gaps may be related to three main issues: how communicational theory within the syllabi is intended, how it is understood and then brought to the classroom and how teaching professionals’ schooling and tradition related to grammar teaching and testing may affect the outcome of the communicational classroom. If managed, they can be the key to bridging grammatical gaps in the future.