This study investigated the specific ways secondary English learners (ELs) and redesignated fluent English-proficient learners (RFEPs) use academic vocabulary that assesses interpretive reading and analytical writing ability. The research examines how ELs and RFEPs, formerly ELs, differ in use and misuse of academic words. The study extends Olson's (2007) work by analyzing how secondary students use academic words correctly and incorrectly. The results indicate that although both groups rarely used academic words, RFEPs used significantly more academic words and made fewer academic word errors than ELs. Qualitative analyses reveal that RFEPs used academic words to add cohesion, details, and precision in their writing to a greater extent than ELs. Findings have three pedagogical implications. First, ELs need more exposure to academic words in writing. Second, ELs need explicit instruction on how to effectively use academic words in writing. Third, ELs need more writing practice in general to become more comfortable with the act of writing so that they will feel more comfortable using more words overall, specifically academic words. Thus, writing should be assigned often. Also, because ELs and RFEPs used few academic words in their writing, both groups need more exposure to and practice with using academic words in writing.