Mobile phone text messages have been used to deliver interventions that support positive
behaviour in many health contexts. School absenteeism is a problem across the world leading to reduced
reading and writing skills and increased likelihood of school dropout. Much of the published research in
both the fields of school absenteeism interventions and text message driven behavioural change is not
based on theoretical foundations and so it difficult to generalise findings from one study into another
context. This thesis describes the development and evaluation of an intervention delivered by text and
picture messages that supports reduced school absenteeism among at-risk youth. This thesis describes the intervention design process and its connections with Social Cognitive Theory, the Transtheoretical Model, Theory of Planned Behaviour and Self Determination Theory. A pilot trial was undertaken to evaluate the technical feasibility of the intervention method and findings informed the intervention and study design that was evaluated in two three-arm single blind pre-post randomised controlled trials. The studies compared the effect on absenteeism of two styles of intervention with a control group. The first sent feedback of recent attendance performance in the form of a graphical scoreboard and the second sent the same feedback together with individually tailored autonomy supporting messages based on recent
attendance that offered praise and motivational content. When messages were sent immediately after
school in Study One, rates of full day absenteeism were reduced by half when compared to the control
group. When messages were sent at the time that students woke up to go to school in Study Two, there
was no significant difference between the groups. While it was hypothesised that students receiving the
autonomy supporting text in addition to the feedback image would have higher perceived autonomy in
school and lower absenteeism rates, there was no significant mediating effect. Moderation analysis found
that the effect of the feedback on absenteeism was especially strong among participants for whom the
primary language spoken at home was Spanish rather than English. These findings further understandings
related to the effect of autonomy supporting messages on perceived autonomy and the timing of feedback
