This study extends the community of inquiry (CoI) framework and self-regulated learning (SRL) theory through an exploration of the structural relationships among existing CoI variables, learning presence (i.e., self-efficacy and online SRL strategy) and learning outcomes in the context of K-12 online learning. To help understand the influence of K-12 mentoring -- which is unique to online learning in the U.S. -- mentor presence is also included. Structural equation modelling of 696 online 8th through 12th graders' survey responses and final grades showed that adding learning presence to the CoI framework helped to explain how these learners translated their online-learning perceptions into cognitive and affective learning outcomes. We also found that mentor presence significantly and positively predicted online SRL strategy, one of the two components of learning presence. Lastly, we established a connection between the CoI model and various types of learning outcomes that are indicators of K-12 online learning success -- though it should be noted that important differences existed between a model based on final grades and two other outcome models. It is hoped that the processes identified in this study will be useful and relevant to K-12 online-learning institutions and educators seeking to improve their offering via a wide range of approaches.