Upper primary school students' difficulties with decimal place value are widely recognised due largely to the availability of assessment tools that accurately identify students' misconceptions in this domain. Yet, many students' decimal difficulties seem to stem from a lack of understanding of whole number place value for which there are few, if any, comprehensive assessment tools at the upper primary school level. The inevitable result of this is that teachers tend to assume upper primary students have a deeper understanding of place value than is often the case and limit their teaching to fairly routine tasks that do not expose student misconceptions. This paper describes the derivation of a research-based, multi-dimensional Hypothetical Learning Trajectory for whole number place value. It explains the process involved in identifying the key aspects of place value and includes indicative examples of the assessment items used to evaluate this.