A highly granular electromagnetic calorimeter with scintillator strip readout is being developed for future lepton collider experiments. A prototype of 21.5 X0 depth and 180×180mm2 transverse dimensions was constructed, consisting of 2160 individually read out 10×45×3 mm3 scintillator strips. This prototype was tested using electrons of 2--32 GeV at the Fermilab Test Beam Facility in 2009. Deviations from linear energy response were less than 1.1\%, and the intrinsic energy resolution was determined to be (12.6±0.1(stat.)±0.4(syst.))%/E[GeV]⊕(1.1±0.1(stat.)−0.7+0.6(syst.))%, where the uncertainties correspond to statistical and systematic sources, respectively