This paper shows that microscopic obstacles like impurities, precipitates, dislocations and grains can have a deep effect on the motion of phase boundaries in shape-memory alloys. Starting from some previous microscopic models [R. Abeyaratne and J. K. Knowles, Int. J. Solids Struct. 24, No. 10, 1021-1044 (1988; Zbl 0672.73041)] and from an empirical smooth rule for the propagation of the boundary, it is shown that the resulting averaged macroscopic equations automatically describe the stick-slip character of observed boundary propagation. This explains some crucial and characteristic features of experimental observations on the rate-independent hysteresis behaviour in these materials. These results should also hold for crack propagation and for the propagation of domain walls in ferromagnetic and ferroelectric materials.