This is common. Be prepared to deal with admin if you give a grade below 60% for a semester.
Yep. Early in the marking period, I try to inject enough fear into the kids that they'll make an effort to learn. Toward the end of the marking period, I can adjust one or two tests to bring up the average. At the end, class participation grades provide a bit more padding if I need to keep admin off my back. It's all about differentiating the group of kids into the ones who work and earn high grades, the ones who try but can't quite get it, and the ones who don't do their work. I'd like to say my grades are always a reflection of what has been learned, but that's not entirely possible in our environment. By the time I see these kids in high school science class, they've had 10 or so years of social promotion. This generation of kids is being cheated of many things, including a robust education.