This study investigated the effect on children's science understanding of Internet-based instruction in which children from around the world in grades 4 to 8 observed the Moon for several weeks and then shared their lunar data internationally to find global patterns in the Moon's behavior. Students in two American and one Australian class took the Comprehensive Moon Phases Assessment as a pre- and post-test. Instruction in the three classes shared some common characteristics such as exchanging data internationally and focusing on finding global patterns in the Moon's behavior. The results showed that overall and in two of the three classes the students' understanding of lunar phases improved significantly. The international exchange of lunar observation reports was effective, although the instruction in each classroom was under the teacher's control and thus varied from place to place. (Contains 1 table and 1 figure.)