The authors investigated effects of metacognitive instruction at different phases of reading scientific texts on elementary school students' scientific literacy and metacognitive awareness. In all, 108 Israeli 4th-grade students in 4 science classrooms read the same scientific texts and completed the same scientific tasks. From them, 3 treatment groups received metacognitive instruction--before reading (beMETA), during reading (duMETA), or after reading (afMETA)--and a control group received none (noMETA). Pre- and posttests assessed students' science literacy, domain-specific knowledge, and metacognitive awareness. Findings indicated no significant intergroup pretest differences but significant posttest differences on all variables. AfMETA students significantly outperformed all other groups, beMETA outperformed duMETA, and noMETA scored lowest. The authors discuss theoretical and practical implications of this preliminary study. (Contains 4 tables and 1 figure.)