We constructed a new taxonomy for inferential thinking, a construct called Integrative Inferential Reasoning (IIR). IIR extends Pearson and Johnson's (1978) framework of "text-implicit" and "script-implicit" question-answer relations, and integrates several other prominent literacy theories to form a unified inferential reasoning construct, that is positioned as a type of cognitive processing disposition. We validated our construct using a researcher-made IIR instrument which was administered to 72 primary-grade students. Participants answered open-ended inference questions about various aspects of visual narratives presented in comic-strip format. We categorized participants' responses as exemplifying one of the levels of IIR: text-implicit, script-implicit, or a combination of both. We used item response models to validate the ordinal nature of IIR, and its structure. Specifically, we fit Masters' (1982) partial credit model and obtained a Wright map, mean location data, and reliability estimates. Results confirmed that the IIR construct behaves ordinally. Additionally, age was found to be a reliable predictor of IIR, and item types (each modeled as a separate dimension) were found to have reasonable latent correlations between the dimensions. This research provides theoretical and practical insights for the pedagogy and assessment of narrative comprehension.