This study explored, with both experimental and correlational designs, the roles of (a) authentic, communicatively functional reading and writing and (b) the explicit explanation of genre function and features on growth in genre-specific reading and writing abilities of children in grades two and three. The genres used for this exploration were informational and procedural science texts. Sixteen grade 2 classes participated, 10 of which were followed through grade 3 (N = 420), in one of two conditions: (a) authentic reading/writing of science informational and procedural texts or (b) authentic reading and writing of these genres with the addition of explicit explanation of language features typical of each. Growth was modeled across six assessment time points using Hierarchical Linear Modeling. Results showed no effect of explicit teaching on reading and writing growth for six of seven outcomes. Similarly, correlational analyses showed no relationship between teachers' degree of explicitness and growth for six of seven measures. However, correlational analyses showed a strong relationship between degree of authenticity of reading and writing activities during science instruction and growth for four of seven outcomes, with an interaction with degree of explicitness for a fifth. Children from homes with lower levels of parental education grew at the same rate as those from homes with higher levels, and findings regarding explicitness and authenticity also did not differ by level of education. These results add to the growing empirical evidence regarding the efficacy of involving students in reading and writing for real-life purposes in the classroom. They also contribute to a growing knowledge base regarding the complexities of language learning in school. (Contains 14 tables and 10 figures.)