Our student arrival and departure tallies are designed to only capture the primary school travel mode (to and from school). Our data system where the tallies are entered has the ability to generate summary reports based on the individual travel tally sheets but the summaries don't account for mixed modes. If you are attempting to capture combined trips, then you will need an instrument that contains numerous mode split combinations. While we too would have liked to capture mode split information, when we weighed the up-side and down-side of trying to collect split info for children via the classroom, we found that the potential for low response rates and low data accuracy was much greater than the tally that is in use today. I will explain our thinking so you understand our position and use it as you like to inform you decision.
The issue you may run into with listing too many combinations is that the instrument becomes too burdensome to administer and provides too many options to the target audience (K-8 students), may overwhelm the students, particularly the younger children. The list of mode choice options would need to be read completely through once so the students know what their options are before they vote on which mode(s) best matches their situation. This requires more time on the teachers part and confuse the students. These issue could impact your response rates and the validity of your data.
To capture mode split, travel diaries are typically used in studies with adults or studies where the adult fills out mode split information for the child. One example of a travel diary is the one used for a subset of the National Household Travel Survey. The upside to the diary is that, when done correctly, it give you the mode split information. The downside is that it requires a commitment level by teachers and students much higher than simply raising your hand in class. While the diary can be handed out at the classroom level, it has to be completed by the individual which means either they take it home or the teachers have to spend more time making sure each child knows what to do. With either option the response rates will go down. Materials that go home with students may not make it back to school within your time frame, if it is returned at all. Additionally, if teachers have to spend more than a couple of minutes on the survey then adhering to the instructions on how to accurately complete the form begin to go down. If you do create and administer a travel dairy, several way to help improve response rates would be to send reminders to return the diaries and offer incentives for returned diaries.