There has been a resurgence in concern about the levels of pupils' oral language skills at school entry. To support and develop these skills effectively an understanding of the key components of oral language is required. We examined the oral language skills of monolingual children in Reception (M[subscript Age] = 57.9 months; n = 126) and Year 1 (M[subscript Age] = 69.07; n = 124) classes in England. Children were recruited from schools that were representative of London primary schools and were assessed on measures designed to tap phonology, core language skills (vocabulary and grammar) and discourse skills, both in the receptive and expressive modalities. Using confirmatory factor analyses, we examined the associations between oral language skills by component and modality for each age group. Oral language was best represented by four dimensions in Reception (receptive core language skills, receptive discourse, expressive core language skills, and expressive discourse). By contrast in Year 1, three dimensions were identified, irrespective of modality: phonology, core language skills and discourse. Our data speak to the importance of capturing these dimensions in assessments and teaching and monitoring their development at school entry. The results also highlighted the foundational role of discourse skills at the start of school.