I will divide the class into groups of 3 or 4 students each. The students in each group will ideally come from different lab 1 groups, so that as much insight from the requirements analysis phase as possible is represented. (This implies that the group members may need to reconcile conflicts between their requirements analyses, to the extent the conflicts imply differing conceptual models. Often the concepts will be the same, though, even where the requirements differ.) Our class discussion of use cases, and the unwritten use cases you have in your heads, should also drive your conceptual modeling.
Each lab group will be given a room with a whiteboard to work in, and should develop a draft conceptual model. At the end of the class period, the current draft should be copied down onto paper. The group should then agree on a process for turning that draft into a more polished one on paper before the lab due date, and turn in a single conceptual model for the group on the due date. (Unless there are irreconcilable differences, in which case multiple models can be turned in.) Note that a model need not be represented in a single diagram. In order to control the size and complexity of the diagrams, it may make sense to illustrate your model with multiple diagrams, each focusing on a specific coherent aspect of the model.
Your conceptual model should include concepts, attributes, and associations.