Much has been written about the influence of various factors that affect learners' retention of course contents in various contexts and at various levels. However, few studies have focused on the factors that may both affect and indicate the organization of materials or contents presented to learners. This study aims to determine the effects of using different types of signaling on learners' retention in the post and delayed tests on the reduction of adverb clauses in an instructed online English grammar class. The quasi-experimental design recruited three groups, each of which included 20 pre-service language teachers. The control group was instructed on reducing adverb clauses with no use of signaling. However, visual signaling such as using texts in bold type was introduced into the materials for the Experimental Group 1, while the Experimental Group 2 used the materials supported with visual signaling in the form of graphic organizers as flowcharts. The scores from a researcher-developed assessment for the three groups were analyzed with a one-way ANOVA. The results of the study indicate that the participants in both experimental groups scored higher than the control group in the post and delayed retention tests; and the Experimental Group 2 scored relatively higher than the Experimental Group 1. Semi-structured interviews uncovered several advantages of using verbal and visual signaling in the materials used for grammar instruction. [This chapter was published in: Jeong-Bae Son (Ed.), "Context-Specific Computer-Assisted Language Learning: Research, Development and Practice" (p102-121). ISBN: 978-0-6486653-0-4. Asia-Pacific Association for Computer-Assisted Language Learning (APACALL), 2019.]