Reading comprehension (RC) is a multi-faceted construct but is often assessed with a single instrument. Previous research has highlighted that commonly used RC tests are only mildly correlated and vary in the skills they assess, including the differential contribution of oral language and decoding to children's performance. Our study, framed within the Simple View of Reading model, examined the contribution of underlying component skills for multiple RC measures and evaluated whether the contribution of decoding and oral language skills changes according to the RC test used and developmental level. Two hundred Slovak-speaking children were assessed across two time points, using multiple RC tests and measures of decoding and oral language skills. The RC tests showed weak to moderate correlations, echoing findings from other languages. At the end of Year 1, the contribution of decoding and oral language to RC was similar in the Slovak transparent orthography. At the end of Year 2, the contribution of oral language had increased threefold, while decoding remained unchanged from Year 1. Crucially, there were also differences between the tests, with some more reliant on oral language. The results highlight the potential benefits of increasing understanding of the differential effects of the component skills in commonly used RC assessments as an aid to interpretation of children's scores. Such an approach could not only identify children with poor scores, but also pinpoint where weaknesses lie in the underlying components so intervention targets could be formulated accordingly.