Reading comprehension is essential in English language learning, yet students often struggle with technical texts in English for Specific Purposes (ESP). In the English for Wetlands course, students must comprehend scientific texts containing unfamiliar vocabulary, specialised terminology, and complex sentence structures. Although Quizizz is widely used as an assessment tool, its role in revealing reading challenges in ESP contexts remains underexplored. This study identified students’ reading challenges and their causes during Quizizz-based assessments. Using a descriptive qualitative design, data were collected through three instruments namely documentation, questionnaires, and semi-structured interviews. The documentation consists of three reading assessments completed by 28 students, questionnaires administered to the same 28 students, and semi-structured interviews with five participants representing high, medium, and low achievement groups. The findings showed that vocabulary challenges, particularly scientific terminology and unfamiliar words, were the main challenges. Limited vocabulary and insufficient background knowledge emerged as the primary causes. Time constraints and technical issues also affected comprehension. For high achievers, they mainly faced time and platform issues, as medium achievers struggled with terminology and main ideas, and low achievers experienced broader vocabulary and meaning-related challenges. It is suggested that lecturers evaluate providing adequate reading time and strengthening students’ vocabulary to improve students’ comprehension of ESP materials.