Reading motivation has been viewed as a multifaceted construct with multiple constituents. Our investigation of motivational multiplicity expanded on previous literature by including motivation constructs (interest, perceived control, collaboration, involvement, and efficacy), text genres, specific versus general contexts, and the self-versus other evidence sources about motivation. We expected that this multiplicity would influence the identification of reading comprehension growth predictors. We obtained pre- and post-interview data, teacher ratings, motivation self-reports, and reading comprehension scores. Interviews showed motivation constructs to be semi-independent. Students’ reading motivations for narrative and information texts were not highly associated; and self-reports and other motivation reports were not highly associated, but situated and general reading motivations were correlated. Interview-based coding of motivation predicted reading comprehension growth, but reading comprehension did not predict motivation growth. Situated motivation for information books predicted general motivation growth according to multiple regression analyses. Implications for an engagement model of reading development were discussed.