Building on current theoretical understandings of how children learn to spell, this paper reports the design and validation of a new pseudo-word dictation test (labelled the Components of Spelling Test: Pseudo-word version) to measure three spelling components underpinning Standard English: phonology, orthography and morphology. For the first phase of the study, the instrument was tested on a calibration sample of 381 students from Grades 3 to 6, aged between 8 and 12 years. Two versions of the test were recursively developed for Grades 3 and 4 (Pseudo-word-G-3-4) and Grades 5 and 6 (Pseudo-word-G-5-6). In the second phase of the study, the calibrated instrument was validated on a different sample of students in Grades 3 and 4 (n = 224) and Grades 5 and 6 (n = 233). The instrument shows high reliability (0.79–0.92) across the spelling components. A key feature of the instrument is that it affords three specific measures of spelling to align with Triple Word Form Theory. This instrument can be used by teachers to screen students with difficulties in spelling and resultantly plan for targeted instruction in school contexts. It can also be used as a measure of spelling ability for experimental, developmental and correlational research purposes. This novel instrument fills a gap in spelling ability research literature by providing the first pseudo-word metric to assess 8- to 12-year-old students’ phonological, orthographic and morphological spelling skills.