When German children from forest kindergartens went to primary school, teachers observed a significant improvement in reading, writing, mathematics, social interactions and many other areas. A yearlong study was done where a group of 9th and 12th grade students learned through outdoor education. The focus was on raising the critical thinking skills of the students as a measure of improvement, where critical thinking was defined to be, "the process of purposeful self-regulatory judgment and decision making". The problem solving capabilities included the ability of students to interpret, to analyze, to evaluate, to infer, to explain and to self-regulate. Researchers found that both 9th and 12th graders scored higher than the control groups in critical thinking by a significant amount.