Yes.  Many times students forget passwords (we all do!).  From the teacher dashboard, a teacher can reset a password (as well as other profile information) for a student by clicking on "Students" tab in the left navigation menu and then upon the name of the student whose password you wish to change.  A pop-up window will appear where you can change the student's password.  Also, make sure your student is logging in using the exact same email address (or username) that is listed in your student roster.  It's not uncommon for a student to unknowingly mistype his email address upon registration, so when he attempts to log back in using the correct email address, he will be inputting an email address that is not registered in the system.