Over the last fifty years, Welsh-medium primary education has developed and flourished across Wales, with an increasing number of pupils from non-Welsh speaking homes taking advantage of the provision. As a result, classes in primary schools may contain a wide linguistic diversity: pupils who are fluent in Welsh, pupils with some knowledge of the language, together with pupils from non-Welsh-speaking homes with no knowledge of the language. Teachers, therefore, have to cope with consolidating and enriching the Welsh of those pupils who come from Welsh-speaking homes on the one hand, while, on the other, having to lay a firm foundation in Welsh for those pupils from a non-Welsh-speaking background. This article discusses implications raised in similar situations within bilingual education systems throughout the world, giving consideration to the advantages and disadvantages of teaching pupils from the opposing ends of the linguistic spectrum in the same class. There then follows an ethnographic case study of how one Welsh-medium primary school has experimented with different methods of grouping and teaching in the nursery/reception class so as to seek to do justice to the differing categories of children within the class; and a number of considerations for further research in the area are raised.