Abstract Experimental results obtained for the one-step channel of the (α, 2α) reaction on 6Li, 7Li, 9Be and 12C at E α = 25 MeV are compared with impulse approximation calculations for the knock-out of an α-cluster from the target nucleus. The effects of going off the mass shell are taken into account; the α-α interaction is described with phenomenological potential parameters deduced from a phase analysis of free α-α scattering. The structure factors are calculated within the framework of the multi-particle shell model with intermediate coupling. For 6Li, 9Be and 12C, satisfactory agreement between theory and experiment is obtained both for the form of the angular correlation functions and for the absolute value of the differential cross section. The assumption of a classical purely “statistical” disintegration of the compound system into three particles without interaction in the final state does not lead to agreement between theory and experiment.