...oh, and one more thing: if in fact all 90 students are in a single course shell, but you're treating them as three separate classes—and if your school allows it—you can create your own sections within the course to accomplish the same Assign To functionality. How do I add a section to a course as an instructor? details the process.
Hello, Rhonda.
[ Edit: Stefanie beat me to it while I was typing and finding links :-D ]
Does your course have sections? If your Canvas instance is integrated with your school's SIS, these would likely already be created for you. If not, you may want to check with the Canvas admins at your school. If you don't have SIS integration, you can create and populate sections yourself.
How do I add a section to a course as an instructor?
How do I assign an assignment to a course section?
If sections exist, but are in separate cross shells, you can cross-list them. How do I cross-list a section in a course as an instructor? (Note: "Cross-listing a section is a course permission. If you are an instructor and cannot view the cross-list options, this feature has been restricted by your institution.")
Course groups can be used in place of sections, especially if your school doesn't automatically create sections from SIS.
How do I assign an assignment to a course group?
Best regards,
Nelson
Hello, Rhonda Arthur
Welcome to the Canvas Community! What you've described is possible to accomplish in Canvas. Whether you're able to do this or not depends on how your "other classes" are defined in Canvas. If each class resides in its own Canvas course, then it's not possible to assign across courses; each course is specific to the students enrolled in it, and only those students can access that course's content. However, if your school permits cross-listing of courses, you'll then have three courses within a single shell, and you can use the instructions in How do I assign an assignment to a course section? to differentiate the due dates between the sections.
Consider reaching out to your local Canvas admin to learn more about the cross-listing policies and procedures in place at your school.
Good luck!