Many students struggle to read multisyllable words (Burns et al., 2017). These students may benefit from additional support to move from the full-alphabetic phase to the consolidated-alphabetic phase of reading acquisition to proficiently read multisyllable words (Bhattacharya & Ehri, 2004). There is limited research on advanced phonics interventions such as syllable instruction which may benefit older struggling readers (Devault & Joseph, 2004). It was hypothesized that the merger two evidenced-based practices, graphosyllabic analysis of syllables with the word boxes intervention, would help students in the consolidated-alphabetic phase improve their multisyllable word reading by providing visual supports for segmenting longer words into syllables. At the time of this study, there was no known research on using word boxes for advanced decoding skills. Therefore, the purpose of this study was to examine the utility of extending word boxes to syllable instruction as a targeted intervention for students who struggle to fluently and accurately read multisyllable words. Five third- and fourth-grade students in a German immersion school participated in a single-subject multiple baseline across participants research study. They received 24 sessions of a syllabication intervention using word boxes and a researcher-developed curriculum of scaffolded scripted lessons. Results on a researcher-developed proximal measure indicated gradual and variable effects based on visual analysis and small to moderate effect sizes using baseline-corrected Tau (Tarlow, 2017). Pre- and post-intervention assessments indicated mixed generalized gains with consistent improvement in word attack skills but increased risk on oral reading fluency. Some participants benefited more than others. Social validity measures indicated participants and research assistants considered the intervention to be acceptable. Given these mixed results, the intervention is not suggested for use in schools at this time. However, there is a need to further research syllabication interventions. Possible improvements to this intervention were identified through this study, which may provide opportunities for future research. Validating measures to monitor student progress in multisyllable word decoding is another potential area for future research. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]