Two studies aimed to address a gap in the extant literature by examining the effectiveness of two positive psychology interventions (PPIs) implemented by teachers in 6-10 weeks on HA and LA students (ability grouping based on scores in a national examination at the end of Grade Six). Study 1 used a quasi-experimental design: two classes from each ability group (n=115) were randomly assigned as the experimental group (EG, Gratitude PPI activities) or control group (CG, self-discovery activities). Study 2 involved the split-plot experimental design: half of the students (n=109) in two HA classes and one LA class were randomly assigned as EG (Hope PPI activities) or CG (self-discovery activities). Comparison of pretest, immediate posttest and delayed posttest scores revealed that the Gratitude PPI improved school resilience and student-teacher relationship; prevented the increase in depressive symptoms, and the decrease in gratitude and peer relationship. The Hope PPI enhanced the students’ life satisfaction and use of deep learning strategies; reduced depressive symptoms; and prevented the decline in hope and intrinsic motivation. The effects of the PPIs on emotional, academic and social outcomes did not differ significantly across ability groups. The results of the study have important implications for schools implementing PPIs.