In light of the difficulties inherent in EFL/ ESL summary writing teaching and learning, it is of paramount importance to probe into the instructional techniques to enhance summary writing ability. This study investigated the relative impact of two instructional techniques: Network Tree Advance Organizers (NTAOs) and Marginal Glosses (MGs) on EFL learners' summary writing ability. First, the Oxford Quick Placement Test was administered to ensure the homogeneity of all of the participants. Sixty language learners were then randomly assigned to three groups: The two experimental groups and one control group. One of the experimental groups was exposed to the MG instructional technique; the other experimental group received the NTAOs; while the control group was provided with neither of them and merely followed the traditional procedures of a writing class. The student-generated summaries at the beginning and end of the instructional period were evaluated by two different raters based on the TOEFL iBT scoring criteria (Baba, 2009). To analyze the date, the researchers used one-way ANOVA and paired-samples t-tests. The results revealed that learners in the NTAO group outperformed their counterparts in the other two groups (i.e., the MG group, and control group). The study points to the relative effectiveness of the utilization of different instructional techniques to promote the learners' summary writing ability. It is also argued that the visual sketch of the materials presented through the NATOs could pave the way for more elaborate and detailed information processing and prompt language learners to properly prioritize, organize, and classify information.