Little is known about the ideal morphology for three-dimensional (3D) porous scaffolds to be used in bone tissue engineering. The present study will supply useful data about the dependence of the mineralization process upon macroporous features of bioactive glass scaffolds. It also points out the difficulty in distinguishing between the bioactive properties of scaffolds if using common characterization techniques often considered as standard techniques to assess in vitro bioactivity. Here, two bioactive glass foams with different porosities (porous diameters and interconnection sizes) were successfully synthesized by varying the surfactant quantity in the sol−gel foaming process. The two foams had porosities apparently sufficient to serve as a bone tissue engineering scaffold and exhibited no significant difference when studied for the releasing or the taking up of ionic species when immersed in simulated body fluid (SBF). However, thanks to microion beam analysis, it was possible to highlight key differences in the mineralization reaction taking place at the surface of the pores. It is clearly evident that the homogeneity of reaction inside the 3D-scaffolds is particularly dependent upon porosity. In particular, it is demonstrated that inadequate porous features can result in limited circulation of the fluid inside the pores. Careful attention must be paid to the pore size distribution and interconnection sizes when designing scaffolds for bone tissue engineering, in order to induce homogeneous mineralization inside the porous material and for the scaffold to be efficiently alimented with nutrients or growth factors while allowing a free circulation of the bone cells.