70% is okay for a grade, but if you ever get a low grade, that's not bad! (Depending on what type of test was it for, if it's big, than I feel bad for you) A grade will understand your knowledge of what you've took it on, and a low grade would show the teachers what you need in order to get a better grade on further tests.
Why wouldn't they? As a teacher, they should ALWAYS look into the grades of the students and make sure that they're able to help said student with the low grades to help you with anything else. If the teachers don't want to help you on a level like that, then chances are, you're not working at a well dome school.
Teachers are there to teach and to give support when needed. It's better for them to do it than the whole internet cause their sources aren't locked behind a payeall or anything like that. You don't have to go through the hassle of looking up said information online when a teacher is good.
I hate seeing users mostly online suffering within the school that they're in. I was apart of one that literally ruined my English so I couldn't understand my full potential, and it harmed my way of making friends.
Now to this day I can understand what other people are saying but not too long ago I literally accidentally named a Terarria world after something innapropirate that I didn't know about
I'm not complete just yet but I am growing my self-awareness as time goes on. I hope that you're able to go through high school just as fast as I am dude. Then you're free from everything. Who knows, college might be a better experience. Don't let the bad grades ruin your day though. At least you still have some friends thay can help you on your journey.