The validity of evidence obtained from classroom assessments in schools is an important concept as significant decisions are made from teachers’ judgments of this evidence. However, what is not clear are the classroom assessment practices that teacher teams use to ensure that the evidence of student learning produced from classroom assessments is valid for their purpose. This qualitative study examined the assessment practices, focussing on validity, from three primary school teacher teams in Australia as they designed classroom assessments in mathematics. From the analysis, four broad themes associated with validity were identified: alignment with curriculum and instruction, catering for student abilities, the scoring rubric and using classroom assessments data to meet students’ needs. These findings could contribute to research and assessment practices in schools that enhance the validity of the evidence collected from classroom assessments.