Youth psychological well-being has become increasingly acknowledged as not merely the absence of psychological distress, but the presence of positive indicators of optimal functioning. Students with complete mental health (i.e., low psychopathology and high well-being) demonstrate the best academic, social, and physical health outcomes. As such, there remains a need to address childrens well-being through a holistic approach emphasizing the prevention of mental health problems and promotion of flourishing. Positive psychology interventions (PPIs) have emerged as a promising method of enhancing students complete mental health. Previous investigations support the utility of multitarget PPIs with middle school students and single-target PPIs (e.g., character strengths, hope) with younger elementary students, though the extent to which comprehensive multitarget, multicomponent PPIs enhance classes of elementary students outcomes relative to a control has not been examined. This study compared levels of subjective well-being, mental health problems, classroom social support, and classroom engagement between students in 6 classrooms randomly assigned to participate in a 10-week intervention targeting a variety of positive psychological constructs (i.e., positive relationships, gratitude, kindness, character strengths, hope) with parent and teacher components, and students in 7 classrooms randomly assigned to a delayed intervention control group. Follow-up analyses examined levels of outcomes of the immediate intervention group relative to the control group at post-intervention, as well as levels of outcomes in the intervention group three months after program completion. At post-intervention, classes of students participating in the immediate intervention group did not have significantly improved student-reported life satisfaction, positive affect or negative affect, classmate or teacher support, emotional or behavioral engagement, nor teacher-reported relationship satisfaction, instrumental help, and emotional or behavioral engagement relative to the control classes. However, several trends were found: (a) students in the immediate intervention group had lower negative affect relative to the delayed intervention control among students with greater baseline negative affect levels, (b) students in the immediate intervention group had lower teacher-reported levels of instrumental help relative to the control among students with greater baseline instrumental help levels, and (c) students in the immediate intervention group reported lower levels of behavioral engagement relative to the delayed intervention control. Because of the lack of improvement in immediate intervention group outcomes relative to the control group at post-intervention, continuation of those anticipated improvements from post-intervention to 3-month follow-up could not be detected. However, there was a significant increase in teacher-reported internalizing symptoms from post-intervention to follow-up among the immediate intervention group (without comparison to a control). Overall, findings from this study do not provide empirical support for the efficacy of a multitarget, multicomponent PPI when delivered universally to classes of elementary students. Nevertheless, high levels of treatment acceptability and feasibility from students and teachers as well as limitations to the study design support the need for educational scholars and practitioners to continue exploring the impact of multitarget PPIs delivered to students in multiple formats and various age levels in order to promote complete mental health across tiers of support and thus optimize success for all students.