Empirical research has systematically demonstrated the predictive role of reading, linguistic and metacognitive skills on reading comprehension performance. The study of the directionality of these relations and their relative contribution in the more advanced grades of primary school is an important aim for reading research, with practical implications for educational contexts. These issues are of particular relevance in semitransparent orthographies such as European Portuguese, as there is empirical evidence that these relations change over time. The goal of this study was to examine the longitudinal relations between oral reading fluency, listening comprehension, vocabulary, reading strategy use and reading comprehension in Portuguese students across grades 4 to 6. For this purpose, reciprocal-causation models with cross-lagged paths were tested using Mplus. The sample included 110 students who completed at least two assessment time points. The results indicated that there is a reciprocal relation between listening comprehension and reading comprehension, as well as between vocabulary and reading comprehension, in every grade. Oral reading fluency was a significant predictor of reading comprehension across grades 4-6, but the opposite relation was not verified. Reading strategy use in grade 5 was predicted by reading comprehension in grade 4. The results are discussed considering previous studies and their potential impact on psychoeducational practice and research. Limitations of the study and guidelines for future research are pointed out.