Assessing Pupils' Progress (APP) arose from a government drive to increase the amount of teacher-based assessment within school and to make this consistent across schools. We conducted semi-structured interviews with head teachers to gain insight into how their schools applied APP and we compared the APP levels for English and Maths, provided by teachers across 11 schools for 72 pupils, to a standardised assessment (Wechsler Individual Achievement Test-II; WIAT). There was a strong correlation between the APP and WIAT for literacy but not for numeracy. Head teacher interviews revealed that APP is used differently across schools and at times is used in a way inconsistent with government guidance, which raises the question of how teacher assessments are used and their purpose. Questions that should be considered are; how is moderation used in schools, what is the function(s) of teacher assessments and what is good practice in relation to these assessments? Clarity about the function of assessments is of vital importance as is ensuring that assessments are meaningful to teachers, pupils, families and schools, especially in light of the weight that can be placed on teacher assessments for all these groups.