This study investigated whether or not explicit metacognitive strategy instruction in English expository texts improved 3rd year bilingual high school students’ reading comprehension of English and Filipino expository texts and their awareness and use of metacognitive strategies. It also sought to find out if such instruction would improve their performance in English, Filipino, and World History classes. Qualitative and quantitative measures for data collection and analyses were used. Results showed an improvement in the students’ Filipino reading comprehension, metacognitive awareness of reading strategies, World History grades, and English grades. But there was no improvement in the students’ English reading comprehension and Filipino grades. Results support the research findings that 1) language affects comprehension (Arafat, 1996) and 2) language skills enhance or enable the effectiveness of the use of metacognitive strategies for comprehension (van Gelderen et al, 2007). Implications are drawn and recommendations made for developing vocabulary and language proficiency in both the L1 and L2, studying the advantages of being a bilingual for the acquisition and use of metacognitive strategies, and conducting similar studies using a longer time frame.