The Spanish writing system has consistent grapheme-to-phoneme correspondences (GPC), rendering it more transparent than English. We compared first-language (L1) orthographic transparency on how monolingual English- and Spanish-readers learned a novel writing system with a 1:1 (LT) and a 1:2 (LO) GPC. Our dependent variables were learning time, decoding, and vocabulary. We found a main effect for transparency. Participants learned LT faster and decoded more words in LT than in LO. L1 reading characteristics influenced learning. English-readers decoded more words in the LO-LT sequence and Spanish-readers decoded more words in the LT-LO sequence. Spanish-readers had more difficulty recalling the meaning of LO than LT words; for English-readers there was no difference between the two word types. Our findings indicate that readers' L1 orthographic transparency or GPC type influences L2 decoding and the learning of L2 words from combined written-auditory teaching.