Within the sleep literature there is limited data on the normative sleep patterns of young adolescents. The current study will look at the relationship between sleep patterns, well-being, and electronic media use among children of young adolescent age living in Aotearoa/New Zealand. Participants included 164 young adolescents aged 11-12 years-old from intermediate schools in Christchurch and Dunedin. Participants were required to fill out a sleep and activity diary to measure their sleep/wake patterns and electronic media use across a typical school week. Parents and teachers filled out a variety of measures to collect data on anxiety symptoms, externalising and internalising problems, peer relationships, and academic performance. Results showed a number of findings: first, nearly half of participants were taking more than 20 minutes to fall asleep and as a possible consequence were sleeping for less than the recommended nine hours; and less than 10% of children meet criteria for problematic night wakings. This suggests that young adolescents experience problems in initiating sleep rather than maintaining sleep. Second, multiple sleep variables were found to be associated with hyperactive/inattentive behaviours, pro-social behaviours, peer problems, and problems engaging in appropriate behaviours for the classroom environment. Third, exceeding the two hour recommended limit for electronic media use on mobile phones and tablet/MP3 players was associated with later sleep onset times and insufficient sleep. Computer/game console use was associated with a delayed sleep phase, whilst television viewing was only associated with later wake up times and night wakings. The results of the present study indicate that sleep is crucial for young adolescent school time well-being, with many young adolescents obtaining insufficient sleep possibly due to their use of electronic media.