Previous research on online features embedded in language assessments have been limited to the use of dictionary or spell/grammar check. Few have examined the role of accessibility features in the Kindergarten to Grade 12 (K-12) English learner (EL) context in the U.S. This study examined how K-12 EL educators perceive and instruct online accessibility features in an annual English language proficiency assessment taken by over 2 million children. Educator perception of ELs' use of the features was also investigated. Of the ten features examined, five (Colored Overlays, Color Contrast, Highlighter, Line Guide, and Magnifier) were available across the four language domains (listening, speaking, reading, and writing) and five were specific to writing (Sticky Notes, Cut, Copy, Paste, and Underline). In a two-phase mixed-methods study, first 377 K-12 EL educators completed a survey and nine educators were further interviewed. Findings were analyzed according to educators': (1) perception of online accessibility features, (2) instruction of the features, and (3) perception of ELs' use of the features. Educators perceived the Highlighter, Line Guide, Copy, and Paste to be more important than others, which affected their instruction. Results provide practical implications for instructing and designing online accessibility features in K-12 English language proficiency assessments.