The Boronated Scintillator Detector (BSD) is a new detector sub-system for the future Cosmic Ray Energetics and Mass for the International Space Station (ISS-CREAM) mission. It aims to complement the instrument’s tungsten calorimeter in identifying cosmic-ray electrons above 100 GeV. Such electrons are of significant scientific interest, but their identification is complicated by the overwhelmingly more abundant hadronic cosmic rays, hence making significant hadronic rejection power of paramount importance. Particle showers initiated by nuclei in the ISS-CREAM calorimeter have a profile different from an electron-induced electromagnetic cascade, and the hadron rejection power deriving from this difference can be significantly enhanced by making use of the thermal neutron activity at late (>400 ns) times relative to the start of the shower. Indeed hadron-induced showers tend to be accompanied by significantly more neutron activity than electromagnetic showers. The ISS-CREAM BSD endeavors to measure this late thermal neutron shower activity by detecting the boron capture of these thermal neutrons in a boron-loaded plastic scintillator, located underneath the calorimeter. Results from a 2012 test of this plastic scintillator in the CERN H2 beam line are discussed, and a comparison of these results is made with the performance predicted by a detailed GEANT4 simulation of the ISS-CREAM instrument.