We analyze the field-dependent femtosecond dynamics of bandedge photogenerated electrons undergoing parallel transport in quantum-well structures. the intracollisional field effect, breakdown of the Fermi golden rule, quantization of the phonon modes, and transient charge variations are all comprehensively included. Our electron heating rates at zero fields are in agreement with experiments. the results are indicative of an adequate description of the electron-phonon interaction in two-dimensional systems. At high fields we observe an energy overshoot structure in keeping with recently observed data, without any real-space transfer.