We find negative average impacts of attending a charter school on math scores for all three grade levels, and on science scores for middle and high schools but not for elementary schools. (educationnext.org)
Average impacts of middle schools were positive and statistically significant throughout the 10 - year period covered by the study, though higher in earlier years than recent years. (mathematica-mpr.com)
Therefore, anything with an effect size greater than 0.40 has an above average impact on students.) (urbanesc.org)