Scandium additions are known to offer a number of benefits to aluminium alloy performance. Many of these benefits can be attributed to the precipitation of fine Al3Sc particles. These particles are fully coherent with the aluminium matrix when they are small, but can lose coherency as they grow or coarsen. In this work, the change in coherency has been studied in an Al- 0.12 wt%Sc alloy over the temperature range 300-425oC. Three coherency regimes were identified, consistent with previous observations. The time and temperature range over which coherency changes occur have been measured for a range of conditions and correlated with the precipitation kinetics and the predictions of a model for Al3Sc precipitation. The effect of the coherency change on the particle morphology has also been investigated.