We have demonstrated AC field-driven mechanical alignment of colloidal CdSe/CdS NRs by measuring concurrent changes in optical transmission. Our work identifies two distinct scales of interaction that give rise to the macroscopic optical response: (1) the spontaneous mesoscale self-assembly of colloidal NRs into bundles with greater optical anisotropy than ensembles of individual NRs, and (2) the macroscale ordering of NR assemblies along the direction of the applied driving field. Ensemble optical anisotropy measurements show that aggregated NR assemblies are more anisotropic compared to isolated NRs, and therefore, provide an enhanced electro-optic response. A key insight from our study is that the field-driven relative change in absorbance depends not only on the degree of NR alignment, but also on the optical anisotropy of the absorbing species-i.e., isolated NRs or NR assemblies. By analyzing our measurements using an optical model that we derived, we have quantified the degree of order in terms of the average emitter orientation relative to the field axis. Our results show a consistent improvement in macroscopic alignment as a function of NR concentration, with a minimum average deviation angle of 18.7° based on our extrapolated values for anisotropy. Our results also indicate that NR bundles are more responsive to field-driven alignment compared to individual NRs. This work provides a basis for quantitative determination of AC field-driven ordering in colloidal NRs and may further aid the design and fabrication of optoelectronic devices with aligned anisotropic nanocrystals.