In this study we aim to analyze the system size dependence of errors due to the adiabatic approximation. We restrict our analysis to electron dynamics generated with real-time TDHF and time-dependent configuration interaction singles (TDCIS) methods. For both methods, the time-independent, ground-state wave functions are exactly the same -the Hartree-Fock wave function. However, the TDCIS method is a wave function based method that does not suffer from errors due to the dependence of the potential on the density that are found with TDHF and TDDFT within the adiabatic approximation. By comparing TDHF and TDCIS, any consideration of electron correlation effects is removed from our analysis. For three molecules ((CH 3 ) 2 N-(CH=CH) n H, n=1,2,3) with increasing π-conjugation, we show that size-dependent effects do indeed exist due to the dependence of the potential on the time-dependent density, specifically in the behavior with a resonant field and in the shifting of peaks in the absorption spectrum. We examine the sizedependence of this qualitatively unphysical behavior to determine if TDHF and TDDFT methods could be more confidently applied to larger chemical systems.