This study was published in 2008 and examined the effect of chess as a mathematics lesson for students with learning disabilities in four German schools. Some classes were randomly assigned to have one hour of chess lessons per week in replacement of one hour of math lessons for one academic year. Students in the treatment and control groups were given a math assessment designed by the authors at the beginning and end of the year to measure their concentration and calculation abilities. The chess lessons were designed specifically for children. Thirty-one students from the treatment group and 22 students from the control group completed the pre- and post-test and were considered in the analysis. The authors found that calculation abilities for counting and simple addition tasks improved significantly more in students receiving the chess lessons. The effect size in mathematics was 0.204 standard deviation units. However, the results were statistically insignificant suggesting no difference between treatment and control students. This study was eligible for inclusion in the systematic literature review and categorized as a Tier I study. The results may not be generalizable to students without learning disabilities, or to students with learning disabilities in larger class sizes (classes in this study had a class size of 8-13 students).