Electron and positron transmission experiments have been performed on MgO and Si single crystals with energies between 5 and 45 MeV. The measured axial directional effects can be interpreted in terms of the classical continuum model of positive ion channeling, if particle deflections caused by string scattering are taken into account. The influence of crystal thickness and particle energy are understood qualitatively by these classical theoretical considerations. Computer calculations were performed to give a quantitative comparison of the classical theory with experimental electron transmission profiles. Fine structure due to diffraction effects has been observed in angular distributions of electrons and positrons up to particle energies of 15 MeV.