Assessing and monitoring the mathematics progress of students is a key role for teachers. It is important for assessment tools to identify students who are not yet thriving and provide guidance for teachers about how to support these students. In our study, teachers assessed 396 Grade 1 students midway through the school year using the Mathematics Assessment Interview and framework of growth points. The findings describe a wide distribution of knowledge across the growth points in each of the number domains. Further analysis showed that at least 30% of students were vulnerable in each number domains, highlighting the need for mathematics interventions.