Physical model tests at small and large scales have been carried out to assess the influence of the model scale on the wave reflection of low-reflective quay walls consisting in prefabricated caissons with frontal openings and internal rubble mounds. Both monochromatic and random waves have been modeled. The experiments have been carried out in the small and large scale facilities at Laboratori d'Enginyeria Maritima of the Universitat Politècnica de Catalunya, in Barcelona. The approach described in Burcharth et al. (1999) for the treatment of scale effects for porous flows has been applied to scale down the nominal diameter of the grain material at small scale (1:33). The results with and without correction of scale effects have been compared with large scale ones (1:4). However, there is not plenty of literature on wave reflection of such kind of structure: Matteotti (1991) and Faraci et al. (2012) carried out physical model tests for configurations similar to the one analyzed in the present work. Altomare et al. (2013a) applied an innovative data-driven modeling technique to analyze the relationship between wave reflection and hydraulic-geometrical parameter for random waves, basing the analysis on the results from small scale tests. A discussion on similarity or differences with the mentioned studies has been conducted confirming that the approach proposed by Burcharth et al. (1999) led to more accurate results. The main aim of the present work is to provide a reliable description of the behavior of such structure exposed to the wave actions, considered remarkable since a similar quay can be implemented as berthing structure inside the harbors. The paper underlines the importance of the treatment of the scale effects in such kind of modeling and the choice of a proper model scale. Finally a new equation to evaluate the reflection coefficient of such kind of structures is proposed.