According to creative writing pedagogies academic Susanne Gannon ("English in Australia, 54"(2), 43-56, 2019), and the Federal government-commissioned NAPLAN review (McGaw et al., 2020), NAPLAN has restricted how writing is taught in secondary schools. A NAPLAN-influenced structural approach to teaching writing has subsumed the development of imaginative capacity. Given the considerable negative criticism of the NAPLAN writing tests, including the negative impact it has had on the teaching of writing, there is a need, we argue, for a fit-for-purpose assessment rubric that assesses creative writing. In a 10-week project, teaching creative writing with three classes of Year 9 students in Steiner schools, we evaluated the use of a novel creative writing rubric, created by published creative writers and lecturers (the second and third authors), to assess the students' creative writing pre- and post-program. Consecutively, the NAPLAN narrative criteria were also used to assess the same writing scripts as a point of comparison. The creative writing criteria privileged craft-based approaches to imaginative writing compared to the function and form-focused criteria of NAPLAN. Statistical analyses of the reliability and validity of the creative writing rubric showed that the construct can be scored with a significant moderate level of reliably by different raters (r = 0.5-0.7; ICC = 0.6). Internal consistency reliability of the criteria was found to be excellent (Cronbach's alpha = 0.94). Content validity of the instrument was found to be strong (r = 0.7-0.9) and significant. Unexpectedly, analyses for concurrent validity showed that the instrument correlates strongly (r = 0.7) and significantly with the NAPLAN narrative rubric, suggesting some overlap, but not parity with the NAPLAN assessment. We found that students' post-project writing improved in all aspects according to the creative writing rubric, with a statistically significant improvement in students' "structural elements and presentation" and group average improvement approaching significance in two other criteria: "words, sentence, and voice" and "characters and context" (effect sizes d = 0.3-0.4). However, there were no significant improvements in the students' post-program writing according to the NAPLAN criteria, possibly because the NAPLAN narrative task criteria did not capture student development of a unique writing style or individual "voice" or other craft-based standards of proficiency measured by the creative writing rubric. Given the validity and reliability evidence, we conclude that the creative writing rubric is a fit-for-purpose guide to school-based learning and assessment of creative writing.