We describe theoretically the process of multi-beam reflection in a two-dimensional electron system with a lateral potential barrier. Due to spin-orbital interaction, the reflection process leads to the formation of three beams with different spin polarizations. The efficiency of spin conversion can become small for smooth lateral barriers. Nevertheless, we demonstrate that the spin-conversion effect remains strong for realistic lithographical potentials and spin-orbit interactions in etched lateral nano-structures. The system with a lateral barrier suggests useful applications as a spin-filtering device. The expected quasi-classical adiabatic behavior without spin conversion is found in the system with a very strong spin-orbit interaction. We also consider the quasi-classical motion of electrons in a system with boundaries in a magnetic field and two magnetic focusing geometries.