This work deals with the use of a compartmental model to interpret the change of the performances of a draft-tube baffled (DTB) crystallizer due to progressive scaling. The examined case was the reaction -crystallization of sodium perborate tetrahydrate. First of all, a model based on both MSMPR and PFR compartments was developed. The model was then applied to evaluate the reduction of the flow rate of the circulation stream through the draft-tube due to progressive scaling, and to predict the relevant crystallizer performances. Finally, the possibility of estimating the scaling extent in the crystallizer from the crystal size distribution (CSD) measured along the run time was shown.