I'm in Texas, and I work in a middle school, not a high school, but here's some stuff that will hopefully be helpful:
My district uses the 1:X model, and each student gets a district-issued iPad beginning in 4th grade. All of our textbooks are online except for math. I think quizzes and tests are primarily done with pen and paper, but most daily grades and major assignments are done online, generally through Google apps. Our district wifi has filters installed for use on district devices, but if kids have their own phones (and most of my students do, as the school is in a rather affluent neighborhood) and data plans, they can basically access whatever they want at school, which, as you can imagine, is great fun to monitor

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As others have mentioned, it varies a lot. This will be my third year in my current district, and in my previous district, they had just gotten around to issuing one iPad per *classroom* right before I left. That district still relied primarily on desktop machines in computer labs, while my current district has laptops issued to classrooms, as well as a laptop cart in the library. So there's not really one universal standard for everyone.
I have noticed that while my students do almost everything on their iPads, when it comes to reading, they prefer paper. I read way more ebooks than they do!
