When you are building a loop and you are in the edit mode, you can choose to lock a hub. Open the hub panel and in the list at the bottom you will see a padlock and it says Unlocked. Click the lock and you will see your options. Click the key if you want to lock the hub so that an individual student can unlock it with a code. Decide what the code is and write it on the line, click the tick and then Save. Remember to think of a way for your students to find the code in the loop. Perhaps is it the answer to the last task in the last node in the previous hub? Notice that all hubs after the one you have locked, will also be locked for your students. When the one you locked with a code is unlocked, the following hubs will also be unlocked.This means that if you want your students to be able to open one hub at a time while working in the loop, you must put a code lock on each hub.