Writing is a complex process that presents challenges for middle school teachers and their students with and without disabilities. A particular area of difficulty is the application of content-area vocabulary in the explanatory writing of sixth-grade students. This two-group quasi-experimental study investigated the effectiveness of an elaborative vocabulary strategy instruction on the vocabulary scores, concept map scores, explanatory writing, and self-efficacy and attitudes towards writing of 104 sixth-grade students with and without disabilities enrolled in an urban charter public middle school. The study was conducted over a four-week period. The results showed that the elaborative vocabulary instruction had statistically significant effects on the concept map scores favoring the experimental group, but generally showed no significant differences in vocabulary, explanatory writing, and self-efficacy and attitudes. The findings of this study support the need for continued investigations in quality vocabulary instruction that impact writing, specifically, teacher training and support in the area of vocabulary strategy instruction to impact explanatory writing outcomes. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]