For CSA purposes child support is payable all the time that Child Benefit is being paid and the child is aged under 16 or
under 19 and in full-time non-advanced education.
The law has recently changed so that in some circumstances CB might be paid until the age of 20, but this has yet to be implemented by the CSA.
Whether CB is paid or not depends on the nature of the apprenticeship. CB is paid if the apprenticeship is a programme-led college course, CB isn't paid when it's an employed apprenticeship.