This study was an investigation of the washback impacts of task-based assessment on Iranian EFL learners’ vocabulary learning and grammatical ability at the intermediate level. For this purpose, 184 male and female students who were in their third year of school were chosen from 12 schools of (X) (X). This election was done via a multistage cluster random sampling technique using the Cambridge Placement Test (2010). All of the sessions were divided into two parts, 20 minutes were considered for teaching grammar and 20 minutes were for teaching vocabulary. The components of this study were Oxford Practice Grammar Intermediate Diagnostic Test and a standard vocabulary test extracted from TOEFL exams between 2017-2020. The researchers prepared a test for every two groups at the end of every three sessions. It was found that by removing the pre-test factor, the covariance, the task-based evaluation’s washback impact makes the grammatical and vocabulary learning of students better. Considering the reality that every academic endeavor contains planned testing and evaluation techniques to maximize academic achievement and progress, the findings hint that TBLA as an academic measurement device can nicely replace the traditional evaluation techniques.
