A qualitative case study was employed to explore the assessment practices of English Language Teachers (ELTs) used in assessing the Oral Communication Skills (OCSs) of the students of Grade 5 in Karachi, Pakistan. The study also aimed to explore the factors that facilitate and the challenges that English Language teachers face during the assessment of Oral Communication Skills. The data were collected by using various tools such as semi-structured interviews, Focus group discussion and classroom observation. Through a purposive sampling, participants were selected for semi-structured interview and focus group discussion. Semi- structured interviews were conducted with two English language teachers, a focus group discussion was conducted with 8 students of grade 5 and classroom observations were also conducted for the triangulation of the data.The findings of the study revealed that assessment practices especially-formative assessment - have a positive impact on students’ learning in the area of Oral Communication Skills. Findings show that English Language teachers use various assessment strategies, such as discussions, oral questioning, interviews, role plays, peer assessment, turn and talk and presentation to assess Oral Communication Skills of students which in turn helps students in motivating and building their confidence to participate in the classroom. Teachers were aware of the fact that speaking of English language can be learnt through practice. Therefore, teachers use these assessment strategies to involve the student in the conversation. Several elements such as technology, listening, lesson planning, reading aloud and integration of all four skills assist English Language teachers in the process of assessment of Oral Communication Skills. Results indicated that speaking skill is the most difficult skill to teach and assess. In addition, it also revealed that English Language teachers face several challenges in the implementation of assessment strategies. The major challenges for English Language Teachers were over crowded classes, negligence of Oral Communication Skills in the summative examination, lack of resources and workload. The generalizability of the findings may be limited to the context where this research has been conducted because of small sample size. However, the findings can be transferred to other contexts having a similar background in terms of teaching, learning and assessment. Moreover, future studies can employ different research methods such as action research or a true experimental study to get more reliable results and see the improvement in students’ learning of oral communication skills.