Ability grouping provides an advanced learning environment for gifted students, possibly buffering them from common long-term increases in academic boredom. We present a 3.5-year longitudinal investigation, spanning four waves of measurement, featuring secondary school students (Grades 5 through 8) from five different German schools with full-time ability grouping (N = 1,861; 55.4% male). We used propensity score matching and latent growth curve modeling to determine the effects of class type on three types of boredom (intensity of boredom, boredom due to underchallenge, boredom due to overchallenge) in two subject domains (mathematics and German). We separated the effects of intervention effectiveness and efficacy, analyzing full and matched sample data. All types of boredom increased over time in both subjects. Ability grouping significantly reduced the intensity of boredom in mathematics in special classes for the gifted ([beta][subscript effectiveness] = -0.158, [beta][subscript efficacy] = -0.206), but had no further effects on the development of subject-specific academic boredom.