We present Monte Carlo results for switching in two and three dimensional Ising models in order to compare with classical nucleation theory. For the case of step-function voltage pulses classical nucleation theory correctly predicts the Monte Carlo results including a cross-over from a thermal nucleation to heterogeneous nucleation due to quenched defects. For triangular wave voltage pulses the coercive field depends on the sweep rate logarithmically roughly as predicted by classical nucleation theory. However the power law dependence on the logarithm of the sweep rate is significantly different from the classical nucleation theory prediction.