The explicit teaching of reading comprehension strategies has been proposed as a means to better prepare secondary school-aged students for today's information-dense, fast-paced, fast-changing global society, and to improve the academic performance of struggling adolescent readers. This proposition of a direct and positive impact of reading comprehension strategies on reading achievement for all students has not been investigated with English language learners (ELLs) who, by definition, do not possess the same level of English language skills as their native-English speaking peers. This mixed-method study investigated linguistic, cognitive, as well as affective factors that impact adolescent ELLs' performance on a standardized state reading achievement test. The quantitative portion examined the relative contributions of second language proficiency and reading comprehension strategies to a prediction model of reading achievement in 110 ninth and tenth grade ELLs. The qualitative portion of the study involved individual interviews and was aimed at deepening the understanding of ELLs' use of strategies during the standardized reading test, while also investigating affective factors that may impact their performance on this measure of academic achievement. Quantitative findings include two statistically significant prediction models of reading achievement with reading comprehension strategies and English language proficiency as predictor variables. However, only language proficiency made a significant unique contribution to the prediction variable. Qualitative findings suggest that the participants had relatively little metacognitive awareness of their comprehension during the standardized test, had overestimated their use of reading strategies as reported on a 30-item strategy survey instrument, had concentrated on sentence-level comprehension due to unknown vocabulary, and may have been hindered by testing anxiety in being able to wholly concentrate on the task. Recommendations made for the instruction of comprehension strategies consist of the raising of metacognitive awareness through the explicit modeling of the thought processes involved in reading comprehension, including determining the meaning of unknown words.