Organisation is a key factor for successful everyday adaptive functioning in schools. Although it is widely recognised that the school environment requires students to be organised if they are to be successful, particularly at the secondary school level, there is currently a lack of instruments available for measuring this construct. To address this, a new teacher report measure of student disorganisation behaviours in the secondary school environment was developed. Following a review of the literature and currently available instrumentation, three phases were implemented: focus-group interviews with primary and secondary teachers; a pilot test of the newly developed instrument to check face validity and item functioning; and an analysis of data from a large scale administration based on the Rasch measurement model. The outcome was a 23-item teacher report scale entitled the Student Disorganisation Scale.