Yes. Often a teacher may want to keep a student in their maths class but also have that student in an intervention group or extra homework club.
Creating classrooms like these are also a great way to make a "view" on say, Pupil Premium students.
Create the new class you want the existing student to also be in.
Go to Manage => Manage students / classes => Create single class.
(If you have Sync to MIS enabled, this button will be called "Create custom class")
For schools with Sync with MIS enabled:
Fill in the text box to name the new class and press OK.
On the page you are then taken to, click on Add an existing student and start typing the student’s name. The system will search and find students with that name. Click the name you want and the system will add them to the new group.
Don't use the "Create a new student" feature unless you are absolutely sure the student does not have a HegartyMaths account already.
Keep adding students until the class has been set up. Important note: the max classroom size in HegartyMaths is 45