After some experimentation, I have found that if I upload the file to an assignment post when I first create it (as opposed to uploading it as "material"), and select the "each student gets a copy" option, a person in a student role in that class can download the file using the method I tried previously (viewing the file, clicking the three dots in the upper right corner, selecting "open in new window" and then hitting the download button there). HOWEVER, if I try to go back to a previously created assignment and "edit" it to include a file that will need downloaded, I don't get the "each student gets a copy" option, only "students can view" and "students can edit" - neither of which will allow a student to download the material.