This study conducted randomized controlled trials to evaluate the effectiveness of an environmental education class and the impacts of nudges and boosts implemented in this program on high school students' basic knowledge, attitudes, and behaviors regarding environmental issues in Japan. This environmental education class consisted of a lecture on reducing the use of plastic products for energy conservation in daily life, a board game for learning how to reduce plastic waste, and a worksheet for reflection. Four types of worksheets were randomly distributed: nudges, in which students were asked to set a goal regarding their level of effort in not throwing away plastic products such as plastic bags, wet wipes, and plastic bottles; boosts, in which participants were asked to write an essay to help increase their empathy for the parties impacted by environmental issues; both nudges and boosts; and none (neither nudges nor boosts). After environmental education, an end-line survey was conducted to evaluate the effectiveness of this class. This study found that the environmental education class significantly improved students' basic environmental knowledge and promoted their concerns about plastic waste. Although there was no evidence that nudges and boosts amplify the effects of the environmental education class on the students' knowledge, nudges were successful in making them more concerned about plastic waste. The results showed that students who received nudges or boosts were more likely to refuse free wet wipes offered at convenience stores but were not more likely to refuse plastic bottles. These results also indicated that interventions through environmental education can change students' pro-environmental behaviors only if the cost of behavioral change is low. The environmental education class not only increased students’ environmental knowledge and attitudes, but the use of worksheets in administering nudges and boosts ensured the effectiveness of environmental education.
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