To add a student to a specific group in a class on Microsoft Classroom, follow these steps:

1. Sign in: Sign in to the Microsoft Classroom at classroom.microsoft.com with your Microsoft account.
2. Select the classroom: Select the classroom you want to add the student to.
3. Create a new group: Create a new group (if you haven’t created one already) for the student.
4. Add the student to the group: Select the group you just created and click the Add Student button in the top right corner. Then, type in the student's name or email address.
5. Confirm student addition: The student will appear in the group list. Click Done to confirm the student's addition to the group.