If you are planning on having mixed registration classes Am and PM it is possible to do this by following the guidance below.
Go to Admin>Config>Core Set Up>Forms
Create your Forms - i.e. YR 1 Set A, YR 1 Set B, this is only a suggestion, as you will have to use the correct Year groups you require. After completing this, go to -
Set your classes up in this area with each child in the correct group. After doing this, assign a teacher to each one, make sure that in register config, that classes and forms are set to yes.
When the teacher goes to the register, it will have a drop down box for form and class. In the morning the teacher would pick the class, in the afternoon they pick form.
Ensure that the correct teachers are assigned in the classes area, as they only appear for the ones they're added to and only teachers who are assigned to the class in the assessment area will be able to see them under home/register/ if done by class (and not form).