The purpose of the present study was to investigate the extent to which portfolio assessment may influence learners’ achievement, their learning process, and their attitude towards assessment for learning English. From the two groups involved in the study, the focus group received portfolio assessment whereas the comparison group received placebo. The instruments used were: 1) pre and post instruction tests, 2) pre and post instruction attitudinal questionnaires for students, 3) self-assessment checklists, 4) questionnaire on portfolio assessment-and 5) semi-structured interview with students on portfolio assessment. The pre and post instruction test data was analyzed through non-parametric Kruskal-Wallis test, which showed a significant difference between the comparison and the focus groups. . In order to see the relationship between self-assessment checklist scores and the progress test scores, Spearman’s rank order correlation showed high correlation between the two sets of scores.