In recent times, and in fact over the past five decades, the importance of teachers’ knowledge of grammar and the teaching of grammar has encountered a resurgence of interest on the world stage as it has done within the research and educational communities of New Zealand (Hudson, 2004; Andrews, Torgerson, Beverton, Locke, Low, Robinson & Zhu 2004; Gordon, 2005; Locke, 2010; Myhill, Jones, Lines & Watson, 2012). Various contemporary studies into teachers’ understandings of grammar and the ways it is taught have utilised the knowledge and experiences of ESL (English as a Second Language) and pre-service teachers (Borg, 1999, 2001; Farrell, 1999; Burgess, Turvey & Quarshie, 2000; Nicholson, 2007; Harper & Rennie, 2008; Basturkmen, 2010). Some studies have emphasised linguistic elements related to the teaching of reading and spelling (Nicholson, 2007; Stainthorp, 2010; Cheesman, McGuire, Shankweiler & Coyne, 2009). However, there appears to be little research involving practising teacher participants, with a specific focus on grammar and its relationship to the teaching of writing. This study explores the broad grammatical knowledge and teaching practices within writing of in-service, generalist teachers of intermediate-aged (year 7 and 8) children. It addresses issues of importance regarding the grammatical understandings, beliefs and teaching practices of teachers within a specific New Zealand educational context. A mixed methods approach to gathering data was utilised in this study. A survey involving 26 year 7 and 8 intermediate school teachers was implemented, followed by a series of semi-structured interviews with a sub-group of six of these participants. The findings of this case study strongly suggest that, although many of the participants were uncertain of how to define grammar and lacked confidence in teaching grammar, their understandings and teaching pedagogies were stronger than they had perceived them to be. A clear majority of participants considered grammatical instruction to be important in improving student writing outcomes, and most revealed that this was an element included within their teaching practices. Findings also indicate that teachers experience distinct limitations in developing their understandings around grammar and grammatical instruction and that their perception of these limitations affects their confidence in teaching grammar. This study also points to a lack of conformity or standard of learning around teacher professional development in grammar. Moving forward, it would be interesting to determine whether there is, in fact, any form of standardised training around the teaching of grammar within and/or across other New Zealand schools, and what this might look like. Evidence from this study suggests that we need to understand more about what New Zealand teachers know about grammar and the teaching of grammar, specifically within school and classroom writing programmes. Future studies in this vein would benefit from including an element of observation as a methodological tool to help validate reported findings, particularly when investigating teachers’ approaches to teaching grammar.