Ensuring that written materials used in behavioral interventions are clear is important to support behavior change. This study used the Clear Communication Index (CCI) to assess the original and revised versions of three types of written participant materials from the SIPsmartER intervention. Materials were revised based on original scoring. Scores for the entire index were significantly higher among revised versions than originals (57% versus 41%, p < 0.001); however, few revised materials (n = 2 of 53) achieved the benchmark of ≥90%. Handouts scored higher than worksheets and slide sets for both versions. The proportion of materials scored as having "a single main message" significantly increased between versions for worksheets (7% to 57%, p = 0.003) and slide sets (33% to 67%, p = 0.004). Across individual items, most significant improvements were in Core, with four-items related to the material having a single main message. Findings demonstrate that SIPsmartER's revised materials improved after CCI-informed edits. They advance the evidence and application of the CCI, suggesting it can be effectively used to support improvement in clarity of different types of written materials used in behavioral interventions. Implications for practical considerations of using the tool and suggestions for modifications for specific types of materials are presented.