Why is teacher assessment biased?

Chartered College of Teaching ¬∑ Why is teacher assessment biased?   I have previously written about how disadvantaged pupils do better on tests than on teacher assessments - and also about how many people assume the opposite is the case (Christodoulou, 2015a). It's interesting that today, we seem to think that teacher assessment will help the disadvantaged. In the late 19th and early 20th century, the meritocratic advantages of tests were better understood than they are today, as were the nepotism and prejudice that often resulted from other types of assessment. In the 19th century, the civil service reformers Charles Northcote and Stafford Trevelyan fought a long battle to make entry to the civil service based on test scores, rather than family connections. In the early 20th century, Labour educationalists such as RH Tawney and Beatrice and Sidney Webb fought for an education system based around exams, because they believed that only exams could ensure that underprivilege