We examined the learning effect of tatami (Juncus effusus var. decipiens), which is commonly used as flooring in the Japanese style room. The research was conducted in two different types of classroom so as to ascertain the effect of tatami: one was a tatami-matted classroom where a group of schoolchildren were given easy calculation problems for thirty minutes (n=260), and the other was a normal wooden floor classroom where they were given a similar set of problems. We were able to confirm a significant increase ( p<0.001) in the total number of answers in the tatami-matted classroom. As to number of correct answers, however, there was no significant difference between the two types of classrooms. As the total number of answers increased and the correct answer rate was maintained in the tatami-matted classroom, it may be concluded that the examinees maintained their concentration better in the tatami-matted classroom than in the wooden floor counterpart.