With the recent upgrade to Sakai 19, there are new Gradebook Statistics options. By default, students can view the grade distribution for each assignment or for the course grade. The video (0:47) below demonstrates how to turn off this feature or you can follow the steps below:

• Access the Gradebook for your course
• Select Settings
• Select Statistics
• Review the following settings and turn off (uncheck the checkbox) as necessary 
  • Display assignment statistics to students
  • Display course grade statistics to students
• Save your changes