Many schools implemented online lessons in 2020 owing to the impact of COVID-19. It is expected that students and teachers will continue to switch irregularly between face-to-face and online lessons during the academic year for the foreseeable future. Therefore, there is great need to develop teaching material that can be easily adapted so that students can perform experiments at home. Recrystallization is one of the most important techniques used for purifying a mixture. Of the crystallization experiments that can be conducted using only commercially available materials, precipitation of urea crystals was chosen. We subsequently devised a crystallization methodology involving the application of an aqueous solution of urea onto an overhead projector (OHP) film, air-drying the film, and sandwiching it in a self-sealing laminating pouch to make decorations of the acicular crystals that were precipitated in a plane. This experiment can be performed in both face-to-face and online classes and is also effective for developing students’ abilities to express their ideas because it provides an opportunity for students to explain what they see using scientific concepts. We found that this experiment was well-received by lower secondary school students and there were no differences in self-assessment regarding the beauty of the crystals between the online and face-to-face lesson students. As this experiment allows students to observe the results in a short period of time and is visually beautiful, it proved to be an effective teaching material for arousing the curiosity and interest of students. We therefore hosted an experimental classroom designed for elementary school students at a local science festival. This “Urea-Crystal Wall Decorations” experiment activity is expected to increase students’ positive attitudes toward science at a time when society is dealing with COVID-19, which has made it difficult to carry out scientific experiments in the classroom.