Diatom fossils are useful indicators in the study of sedimentary environments, but observations of them are not popular in schools. Here I explain a method of reconstructing a sedimentary environment by using diatom fossils observed in boring samples from Hyogo Prefectural Amagasaki Oda Senior High School located near Osaka Bay. The depositional environment was clarified by comprehensively examining the results of a sulfur analysis. It is hoped that diatoms will be actively utilized in classes by observing them at many schools and collecting the obtained results.