The influence of atmospheric conditions and the day of the week on school children's behavior was investigated by undergraduates. The college students were told either that their participation in the research was compulsory and would be graded, or that their participation was voluntary and ungraded. Fifty teachers observed their pupils' behavior and completed observation scales twice daily. When the college student researchers knew that their report of the teachers' observations would be checked, the reliability of their data collection was 100 percent. When the students did not know their reports would be checked and their research was ungraded, 14 out of 47 faked their observations. Ten other students began the research but stopped after 1 or 2 weeks. It was found that the weather influenced the behavior of the school children. The higher the air pressure and the greater sunshine hours in a day, the quieter the children were. However, the more humid it was and the heavier the rainfall, the more active the children were. In addition, on Monday morning they were quieter and on Friday afternoon they were more active. (SW)