Students with accounts on CodeHS can be enrolled in multiple sections. If students are taking multiple periods of CodeHS, they are able to join other sections without leaving any of the sections they are currently enrolled in. Teachers for all of the students' sections will be able to see their progress.
The best way for a student with an existing CodeHS account to join an additional section(s) is for the student to sign into their account, and then go to the Join a Section link located under Resources on the left side of the Navigation Panel.
For more information on switching between sections, check out Students Switching Between Sections.