In this paper we study weak decays of D and Ds mesons emitting pseudoscalar and axial-vector mesons in the ISGW (Isgur-Scora-Grinstein-Wise) quark model using a factorization scheme. Branching ratios for the Cabibbo-angle-favoured decays are calculated. Like the BSW model, here also the calculated branching ratios are smaller than the observed values by a factor of 2-5. We discuss the missing physics that may bridge the gap between theory and experiment.