The purpose of this study was to obtain research-based evidence on the relationships among general characteristics, family strength, self-control, and happiness among late school-aged children using a correlational research design. Methods: The participants were 172 fifth-and sixth-grade students from two public elementary schools. Data were collected by employing structured questionnaires, including the Korean Family Strengths Scale for Strengthening Family II, a self-control scale, and a happiness scale. Data analysis was conducted using SPSS version 23.0. Results: The level of happiness of late school-aged students showed significant correlations with family strength (r=.78, p<.001), and self-control (r=.59, p<.001). Family strength had a significant positive correlation with self-control (r=.55, p<.001). The factors with a significant impact on participants' happiness were family strength (β=.63, p<.001), self-control (β=.21, p<.001), exercise frequency, and self-perceived health. The total explanatory power of the model was 69%, and the explanatory power of family strength for the level of happiness was 61%, showing that the family strength was the most important factor that promoted happiness in late school-aged students. Conclusion: These findings imply that improving family strength is an important aspect of promoting happiness among late school-aged children. Interventions to strengthen late school-aged children's self-control are also necessary.