Finite element analyses of the overall mechanical response of metal–matrix composites are carried out using three different models: standard crystal plasticity, crystal plasticity appended with a tangential continuity condition on the plastic distortion at matrix/particle interfaces, and a field dislocation mechanics model accounting for the presence and transport of polar dislocations. The focus is on assessing the effects of particle shape and size on the work hardening of the composite, as well as its loading path dependence. To a different amount, all models account for shape and size effects, and retrieve the Bauschinger effect. In standard crystal plasticity, the origin of these properties lies in Hadamard's compatibility conditions at the matrix/particle interfaces, but the size effects cannot be quantitatively predicted due to the absence of an intrinsic length scale. Supplementing crystal plasticity with the tangential continuity of the plastic distortion strongly enhances the particle shape and size effects, and the path dependence of the overall mechanical behavior. However, only the additional presence of polar dislocations in the third model allows quantitative prediction of the effects of size, by adding internal length scales (in relation with lattice incompatibility and dislocation transport) and dislocation microstructure building to the description of composite material straining.