Proficiency in spelling is a key influential factor in success with compositional writing, reading, and vocabulary knowledge. To facilitate student learning in spelling, educators should utilize spelling assessment systems that generate useful diagnostic feedback and that are informed by current theoretical underpinnings of learning and instruction in spelling. Nonetheless, within the vocational education and training (VET) sector, there is a notable lack of robust adult writing literacy measures, particularly in the domain of spelling. Assumptions about the nature of spelling development have important implications for the way spelling is assessed and taught. This chapter considers the importance of learning to spell and compares linear and nonlinear theoretical perspectives on spelling development. Assessment systems used for measuring spelling ability are then discussed in terms of their theoretical underpinnings and their suitability for VET contexts. Recommendations for spelling assessment and instruction in VET contexts are offered.