The strengthening of age hardenable aluminium alloys can be achieved by the highly dispersed precipitation of metastable and/or stable phases. Scandium (Sc) as an alloying element has been understood to improve the mechanical performance due to the formation of Al3Sc strengthening phase. The mechanisms of precipitate strengthening can split into particle bypassing and shearing. The former occurs when particles are strong that dislocations can only bow and bypass them, leaving behind Orowan loops, while the latter occurs when particles are weak that dislocations can cut through. Different from bypassing that the critical parameter is the inter-particle spacing, the shearing involves a more complex microstructure dependency. This work introduces our recent modelling development and the associated validation on the age hardening behaviour in Sc-containing alloys, in which Al3Sc is considered as the dominant strengthening phase.