No additional parts are required. You can build structures, mechanical contraptions, and robotic mechanisms all with these 4 connectors. Custom parts can be provided to make it easier to use but you can build a model of anything with those 4 Strawbees connectors.
Teacher Resources:
Lesson Plans and ideas - for Math, Science, Robotics, and Civics
Exploration Ideas - for Communication, Problem Solving, and Habits of Learning
Demco MakerHub - lesson ideas for Science, Math, Art, Engineering, and Robotics