This study was conducted to compare the concentration and emotional condition of elementary school students performing an intensive assignment in the presence or absence of foliage plants, using electroencephalography (EEG) and a modified semantic differential method (SDM). In a crossover experimental design, 30 elementary students performed a 3-min intensive age-appropriate arithmetic assignment in the presence or absence of foliage plants. Continuous EEG monitoring in the frontal lobe was performed using a wireless dry EEG device. Immediately thereafter, subjective evaluation of emotions was performed using the SDM. The concentration of the male elementary students was significantly higher when the assignment was performed in the presence vs. absence of plants as evidenced by the increase in the ratio of spectral edge frequency of 50 and a decrease in the relative theta power spectrum in the right frontal lobe. The SDM results revealed a significant psychological relaxation when the assignment was performed in the presence of plants. Therefore, the presence of foliage plants in the space where the elementary students performed the intensive assignment led to positive effects on concentration and emotional condition.