We report on the scaling behaviour of the colossal negative magnetoresistance effect (CMR) in a single crystal of the bilayer manganite (La_0.4Pr_0.6)_1.2Sr_1.8Mn₂O₇. The high Pr content is responsible for the absence of long-range ferromagnetism and for a CMR effect in the order of 10⁶. The system is down to the Neél temperature (T_N = 50 K) in a superparamagnetic state with spin clusters extending over 6–9 unit cells. The coefficient C, which describes the magnetization-induced resistance drop in the paramagnetic state, has absolute values up to C = 15 at 100 K. The temperature dependence C ∝ T⁻¹ is explained by spin-dependent hopping between magnetic clusters. Spin-dependent scattering and Kondo-lattice models do not account for the magnitude of C and its variation with temperature.