The number of times children change schools, or student mobility, is associated with multiple adverse outcomes across the life span. This study used administrative data from the Western Australian Department of Education for public primary school students who completed Year 6 between 2016 and 2019 to examine potential associations between student mobility and academic (using National Assessment Program -- Literacy and Numeracy [NAPLAN] participation and scores) and behaviour outcomes (measured through school suspensions). The odds of participating (vs. not participating) in NAPLAN were significantly lower for students with high mobility. High mobility students also achieved significantly lower scores, on average, on NAPLAN literacy and numeracy at Year 3 and Year 5 compared with low mobility students. However, there was no evidence of an association between student mobility and school suspensions. These findings highlight the need for action to address substantial academic detriment for mobile students, many of whom are likely to be from lower socio-economic backgrounds. Furthermore, current policies to address academic disadvantage are likely to exclude those students at substantial academic risk and require revision to be appropriately triaged.