Activities (even hidden activities) automatically appear in the gradebook when you create them. If you have some activities that you don't want to delete, but also don't want in the gradebook, you can put them in a folder in the gradebook and set the mean to zero. Before you decide to create an Ungraded category, we always recommend simply deleting unused items from the gradebook or setting their Maximum grade to 0/None if possible instead of using this method.
For a permanent link to this information, please use: http://go.illinois.edu/MoodleGradebookUngraded