In recent increase of social interest for ecosystem conservation, various field education programs have been conducted. However, reports for evaluation for the effect of the education for children has been limited. Tidal flats, which have diverse organisms and safety field for children, are suitable place for the environmental education. In this study, educational effects for children by classroom lectures for tidal flat organisms and field trips in the tidal flats were analyzed by questionnaires using the text-mining and the principal component analyses. Results suggested that motivation for observation was increased after they took the field trip, especially when they watched active behavior of tidal flat crabs. No clear education effect was detected when they took only classroom lectures. Thus, it could be concluded that field observation using the crabs is more effective to increase of interest for tidal flat environment. I will conduct further studies what senses (optic, auditory, gustatory, tactile, and/or olfactory) of children are more active during the field observation, for development of field education programs.