In my nation 16-year olds may work outside of school hours (school is mandatory until they are 18 years old). There are other hard limits on which types of jobs and the time of day they may work. Work shall never interfere with school.
Which suggests that the child labor laws for 16-year-olds are there to keep 16-year-olds in school, rather than school being there as a place to put 16-year-olds who are banned from employment.