We present the comparison of light-scattering calculations between a rigorous solution and the discrete-dipole approximation (DDA) for two-sphere aggregates. We also compare theoretical predictions with laboratory scattering measurements to examine the validity of the numerical solutions. It is found that there are cases in which the DDA solution, while satisfying the validity criterion for interdipole spacing to be small compared with the wavelength of incident radiation, deviates significantly from the rigorous solution and the experimental results. We show that the DDA works reasonably well for small-volume structures and that its validity is challenged, at least as it is currently implemented, when used on larger structures. We also show that, besides its advantages in reliability, the rigorous solution approach is far superior to the approximation method in computing efficiency as well.