For students of English as a Foreign Language (EFL), reading exercises are critical not only for developing strong reading comprehension, but also for developing listening, speaking, and writing skills. Prior research suggests that social, collaborative learning environments are best suited for improving language ability. However, opportunities for English learners to collaboratively practice reading comprehension are minimal, and due to resource constraints and a lack of accurate evaluation methods, English instructors rarely assess student literacy effectively. In response to these problems, we propose a Tag-based Collaborative reading learning System (TACO) that makes use of Web 2.0 Internet social tagging techniques to provide a collaborative environment for reading English. We test our system's ability to both improve reading comprehension and aid teachers in accurately assessing literacy by conducting a three-month trial with 56 participating Taiwanese high school students from February to May 2009. During this period, post-testing results show a significant improvement in reading scores among participants in our tag-based system, and survey feedback from teachers suggests an improved capacity for literacy assessment. (Contains 5 tables and 11 figures.)