Photometric and spectroscopic observations of a very large flare on AD Leo are presented. A self consistent model of a flare corona, transition region and chromosphere is developed; in particular the chromospheric temperature distributions resulting from X-ray and EUV irradiation by coronae of various temperatures are determined. The predicted line fluxes in Hγ are compared to the observed line fluxes to find the coronal temperature as a function of time during the flare. This run of temperature with time is then compared with the predictions of an independent theoretical flare model based on a dynamic scaling law (see paper by Fisher and Hawley, these proceedings).