This applied dissertation was designed to provide a better understanding of the effectiveness of out-of-class safety net corrective instructional activity practices conducted beyond regular classroom instruction for lower secondary level (9th- and 10th- grade high school) students within mastery learning educational environments. The study was designed to shed light on the impact and implications of these practices on Bloom’s vanishing point (Bloom, 1971) and Arlin’s leveling effect (Arlin & Westbury, 1976). Seven mastery learning structured international schools in geographic proximity, of similar size, and utilizing the same program of study were used in this study. Three of the schools that employed a safety net program were the basis of this study, and the four schools that did not have in place a safety net program were used as a control for this observational research. Normed Measures of Academic Progress (MAP) RIT scores (Northwest Evaluation Association, 2005), grade point averages, and safety net program data were used in a series of case-control tests to determine the effectiveness of out-of-class corrective instructional activity safety net programs for above-average and below-average achieving students. The mean study and control group RIT percentile ranking scores for the students was nearly 1 standard deviation above the averages reported by the Northwest Evaluation Association (2005), so these relative comparisons involved bright students. This large volume of data enabled analysis of the effects of out-of-class safety net activities on school-wide and individual improvement in literature, writing, mathematics, and comprehensive results. Series of conclusive nonparametric analysis were used instead of normal distribution tests because of the out-of-bounds skewed nature of the data. Analysis of the data suggested that safety netting programs benefit all students, irrespective of whether or not students received out-of-class corrective instructional activities. The MAP RIT scores of below- average achieving students were not affected by attending a school with a safety net program but their GPA results improved in all subjects. Arlin’s leveling effect (Arlin & Westbury, 1976) most likely accounted for improvement of MAP RIT scores for above- average students who attended a school with a safety net program but their GPA results were not affected. These contrasting benefits masked the school-wide test results, which suggested that a school district might not realize an overall increase in MAP RIT and GPA results when adopting a safety net program. Students identified in need of safety netting services benefited by having been placed in the program up to twice in any respective course, but a point of diminishing returns was reached when a student fell 3 or more units behind in a course in relation to the progress of the class.