Once the teams have a map that shows their reasoning about a problem, they test their ideas. Depending on the investigation, they collect data, look up research, and make observations that will support their causal maps. In the current example, one team might start monitoring the local traffic from the sidewalk or on the Internet. Another team might go to the Internet to find out if there is research literature that supports their tentative relationship between the amount of snow and the number of accidents.
Armed with their data, the teams modify their maps to reflect their new knowledge and opinions. They enter their evidence into the description box for each relationship. It could be the actual data, references to the literature, or a record of observations. At this point the students are challenging each other to verify their reasoning. For each arrow on the map they should agree that they have sufficient evidence to support the relationship.
Some of the initial relationships may prove more complex than originally conceived. Students may refine initial relationships. The students in this example found that while increasing rain increases accidents, the first rain after a dry spell increases accidents a lot.
At this point the teacher might ask the students to print their maps and to write a reflection analyzing the critical factors that influence traffic jams.