Each PocketLab sensor can only connect to one device at a time. Save trials to share data between groups.
If you assign students a Lesson that contains a Collect Data card, any trials they save will be shared with their group. One student in a group should connect their PocketLab to their computer, phone, or tablet, then record and save their Trials.
Clicking Group Work at the top let's you change the card between Group, Individual, and Class work. For Data Collection you will almost always use Group Work. Individual Cards will only let the student who records the data see their saved Trials.
Use Class Work if you want every student to see each Trial that is recorded from everyone. This is great for recording demos in front of the class, or for scenarios where each group is testing something different.
For more information about collecting data and assigning lessons to students, see these articles: