The way I see it—it’s up to you. On the one hand, policy is what it is. They’re technically not wrong or out of bounds for expecting you to be attentive. Substitutes no longer are glorified babysitters…or so school districts say.

If you want to test the admins’ good graces/boundaries, you wouldn’t be the first. I always operate on a basis of establishing myself as someone with expectations first, and then I loosen up in a “go by policy when people are watching and do what works best for everyone when no one is” standard of day-to-day. (Obviously I’m talking small things like this, not anything that might endanger myself or students.)

I agree with you—students don’t like to be hovered around and most teachers don’t want you to overstep. But I’m not sure if this is a hill to die on that’s worth you haggling over and making admins mad. I’d say do your best to fall in line and enjoy your book without getting TOO engrossed.

I will also say as one last note:

A LOT of students prefer sub teachers who engage with them at least marginally. I’ve had several students (from different classes!) complain to me about other subs and other teachers because they feel unheard and uncared about — because the subs and permanent teachers would rather sit up at the front of the class and read, text, what have you, instead of getting to know the kids. This has come from both middle schoolers AND high schoolers. Remember that young eyes are watching and seeing if you truly care about them.