This article uses model materials to introduce a controlled, location- and manufacturer-independent internationally accepted method for assessing shredding machines based on large-scale tests. Furthermore, a better understanding of the comminution behaviour of shredders with fixed settings (gap width, shaft speed, cutting tool geometry) is in the focus of the present investigation and assessed, using the statistical analyses for particle size distribution in certain screen sections. Conclusions have been drawn on the comminution behaviour in general and the material–material interactions of different fractions in the grinding chamber of the shredder by showing significant differences in the pure fraction’s comminution behaviour against the mixture’s comminution behaviour. In addition, the effect of the wear condition of the cutting tools on the particle size distribution has been investigated using statistical tests. As a result, interactions of the materials in the shredder grinding chamber can be demonstrated. The null hypothesis of the statistical test can be rejected due to the p-values, which are around 0.01 and therefore less than the predetermined alpha, which is 0.05, meaning that the shredding behaviour of pure fractions and those in a mixture is different. Additional investigations of waste wood only have shown that the wear condition of the cutting tools does not exhibit any effect on the particle size distribution of waste wood, as seen in the p-value (0.29), which is higher than the used alpha value. This could mean that the cutting tools need to be changed less frequently, which could have a positive effect on plant operation.