True, but if someone can do that but not build on it with the second line, then no other class is suitable for them and they'll turn up at yours.
In that sort of scenario I would set the 'I can set up and crochet a beginner line' lot, the task of producing each stitch perfectly uniformly sized, which slows them down, while developing useful skills, while I got the total beginners set up and started.
Those that manage it, have just produced examples useful to show the total beginners who aren't there yet, what they will later be aiming for, and why having uniform stitches makes a real difference when we get to row two.
A decent tutor will work to ensure no one is left behind, but there is also some responsibility to speak up if you are struggling. If the tutor's done their job properly in creating the atmosphere, it shouldn't be difficult, even if it's just to shake your head when asked how it's going.
People will always be at different levels, with some scared of failing, and others scared of not being the best. It's the tutors responsibility to raise the total beginners up, while deepening the slightly more knowledgeable's skills, but ensuring all concepts are being taught equally to both, and diverting competitiveness into something more useful to the group dynamics.
Everyone is on the same pathway, regardless of where they start, and part of the tutors job is to balance out the personalities and skill levels, so that everyone is seen, appreciated, and acquiring skills at the levels they seek, as well as able to feel comfortable and appreciated in the group, and not overwhelmed.
Being able to continuously differentiate and 'hold the group' is an essential skill that tutees have a right to expect from a tutor.
(I teach a range of art, theater, craft, cooking, tool use, and practical skills, mainly but not exclusively, to people who are homeless.)