Assessments in Task-based learning should be based on tasks, not on language points. It is not effective to teach lessons centered on task completion and then ask students to write a grammar test.
Task-based assessment can be in a variety of forms, including tests and performances. Any task could be assessed, so teachers have ample opportunity to evaluate student progress.
Tasks in assessments should follow the same rules as the tasks frm the lessons. They should focus on meaning and be related to the real world.
Students should be assessed on their ability to complete the task, not on the language production. This, however, can be altered depending on the program or course. Teachers may decide to add a language element to the assessment. When assessing students based solely on task completeiont,it is kmpartant to consider the impact of the interlocutor (Person involved in the task, often as facilitator). This person can affect the student's score. From Peter Skehan:
“We have to consider the possibility that the score assigned to a candidate may not reflect candidate performance only, but may partly be based on biases and limitations arising from raters and scales.”
Skehan (2001: 168)