Hatchery spat of pen shells is difficult to obtain as production runs generally fail. We present a case of commercial pilot spat production of Atrina maura in the hatchery, describing each phase in detail and determining the growth of larvae and postlarvae using multi-model inference (MMI). Growth rates of larvae in D-veliger to umbo stage (D-larvae = 65 ± 5.1 μm height and 75 ± 5.1 μm length) increased from 4.33 μm d-1 up to 675.6 μm d-1 during postlarvae stage (spat = 10.9 ± 2.2 mm height and 28.1 ± 4.4 mm length). Survival presented a significant daily decrease from 22.5% (beginning) to a final absolute survival of 0.042%. Hence, 50,000 commercial spats were produced from 120 million D-larvae. MMI showed that the best-fitting model describing growth corresponds to a Gompertz model for shell length and an exponential model for shell height. Critical phases were transitioning from D-larvae to the umbo stage (>80% collapse of cultures) and high mortality during metamorphosis. Further studies are required to find solutions to these problems. The results of this study may contribute to improving the management of pen shell production in the hatchery, as the production protocol is different from those used for other bivalve species.