We discuss the reaction mechanism associated with two-particle transfer reactions in a simple one-dimensional model. The reaction process is generated by two colliding wells and we follow in time the evolution of the two-particle wave function, initially concentrated in one of the two wells. At the end of the process one can single out the population of the different final channels, including one and two-particle transfer. When a residual short-ranged pairing interaction among the two particles is included in addition to the moving potentials, one observes a clear enhancement of the pair transfer as compared to the expectation of a pure sequential one-particle transfers. The final "exact" solution can be compared to the one obtained within different reaction and structure models (as coupled-channels, first-order approximation, approximate treatment of the continuum, etc), so providing important information on the reaction mechanism associated with the different processes.