This study examined the effects of Reading Intervention for Adolescents (RIA) and a mentoring intervention (MI) implemented for 1 year with ninth-grade English learners (ELs) with reading difficulties. Eligible students enrolled at three urban high schools were randomly assigned to the RIA (n = 142), MI (n = 163), RIA and MI (n = 164), or business-as-usual comparison condition (n = 154). The RIA lessons focused on advanced word study, fluency, academic vocabulary, and collaborative comprehension strategies with content area texts. The MI assigned each student a mentor who helped them access and participate in school activities with the expectation that this condition would be associated with improved self-perceptions toward school engagement. RIA (RIA and RIA + MI) had significant, positive effects on sentence-level fluency and comprehension (g = 0.17) and vocabulary learning (g = 0.30), but not on measures of word reading, vocabulary, or reading comprehension (g range: -0.1 to 0.05). The MI intervention did not yield discernable effects on students' self-reported engagement questionnaire, absences, course failures, or disciplinary referrals. We present considerations for how to address systemic changes for meeting the needs of ELs with persistent reading difficulties in high school.