Proficient communication, particularly reading comprehension, is vital for career progression, yet many college-level English as an Additional Language (EAL) students encounter hurdles in this area. Weak reading skills can impede job prospects, underscoring the need for tailored interventions during students' studies. Therefore, post-entry language assessments (PELAs) can serve as essential tools for post-secondary institutions, aiding in identifying and supporting students struggling with English proficiency. PELAs adopt a diagnostic approach, facilitating language development while maintaining educational experiences. Despite increased interest in PELAs, few diagnostic assessments cater specifically to reading proficiency. This paper explores the creation of a PELA for first-year college students in Canada, designed to prepare them for diverse workplaces. Utilizing Evidence-Centered Design (ECD) ensures validity in assessment development, emphasizing inference-based reasoning from individuals' responses. Insights from a task survey with 12 professionals underscored the significance of understanding instructional texts for academic and professional success, informing the development of a diagnostic reading assessment beneficial to both multilingual and L1 literacy students.