In a recent paper by the same authors, we have thoroughly described how to extend to the case of general shells the well known D.K.T. methods (i.e. Discrete Kirchhoff Triangle) which are now classically used to solve plate problems. In this paper we have also detailed how to realize the implementation and we have reported some numerical results obtained over classical benchmarks. The aim of this paper is to prove the convergence ofa closely related method and to obtain corresponding error estimates