The present study was conducted in three parts. Each part analyzed theory of mind (ToM) development in children who are deaf in relation to mental verb and complement syntax understanding. In the first part, participants were given a series of tests for the purpose of correlational analysis of ToM, mental verb understanding, and memory for complements. The second part involved a training program using separate book-reading sessions and discussion sessions. The third part analyzed the impact of language modality on the program's efficacy. Direct positive relationships were seen between ToM development and vocabulary, complement syntax mastery, and mental verb understanding. Furthermore, a principal goal of this study was to examine whether training children using mental verbs and complement syntax could facilitate (a) their understanding of mental verbs, (b) their memory for complements, and (c) their ToM understanding. In sum, these three competencies increased over the entire training program. Participants saw a significant increase in complement syntax understanding after the book-reading sessions, which were administered first. Conversely, mental verb understanding and ToM understanding were not significantly changed. However, after administration of the discussion sessions, mental verb and ToM understanding were also increased while complement syntax understanding did not further change significantly. Also, two groups using differing communication modalities (i.e., spoken English and Signing Exact English) were compared. Both groups received a false belief pretest, the book-reading program, and a false belief posttest. Both groups showed significant improvement in false belief pass rates after participating in the full book-reading program. Whereas signers began the program with significantly lower passing rates than speakers on the false belief measure, these signers exhibited overall slightly higher pass rates on the posttest of false belief understanding compared to their speaking peers. [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.]