In "My Classrooms," click on the eye icon at any time to preview the student view.
The student view shows what all students in that class see. (Note that this is not to see specific student work- to view that, click the "Student Work" button directly to the left of the preview icon.)
The students will only see what you've assigned to them. For example, if you've only assigned Lesson 1, but not Lesson 2 or 3, the student will be see this:
You can control what your students see here.
What if my class doesn't have a preview icon?
The student preview icon appears only after students have joined the classroom. If no eye is there, that means no students are in the classroom yet. Need assistance inviting students? Refer to this article.