Make it explicit. Stand at the front, where you usually do (I presume), and say in a big loud voice that you are aware that many of the students in front of you

Make it explicit. Stand at the front, where you usually do (I presume), and say in a big loud voice that you are aware that many of the students in front of you are used to doing everything themselves, without help and without asking for help. And that this does not carry over and here the rules are different and they are now expected to ask questions and seek to discuss, even if they already understand, because an academic tutorial is not just extra lecture time, but a socratic expansion of understanding that every - EVERY - student benefits from, and leaves knowing more than they did when they went in. You might (will) have to say it more than once, and very explicitly, because they are used to hearing well-meaning similar statements that they have learned to ignore. But just say it, explicitly. They're not stupid; just conditioned. Breaking through that conditioning is hard, so hard. The rich kids see your office-hours as a right (and, as I expect you know, see extensions on deadlines and arguing their grades up and being entitled to second chances as a right), the poor kids don't really believe they exist. Breaking that conditioning is possible, so long as you can see it to hit it.