As a (5th grade Math) teacher, I choose a problem level (out of 80+ available), number of problems and a due date. When the students log in, they see the assigned homework(s). The web site accepts submissions from all, grades them and I can see the scores, along with submission date and time taken, for all students in a tabular form.
It is free for teachers. Students pay about $2 per month. You may be able to get a discount.