I have a 16-year-old who is very smart, and his teachers have bragged about his writing capabilities since elementary school. But now, in 10th grade, his A's changed to B's, and some B's to C's and D's. I yell at him and get very angry. He says I'm trying to make him as smart as I am. He's intelligent, but he doesn't care. Is this just a phase?
It is just a phase, and you have to be careful, or it could turn into a permanent condition.
Tenth grade is the time that independence becomes a core issue and focus. Many 10th graders have to push adults and activities away from them, sort of to clean their plates. Then they re-decide one at time what to bring back into their lives. (This is like what happens in 7th grade but exponentially more so.)
Stop nagging him. It's already becoming a power struggle, which in order for him to win will mean he has to fail at school. This doesn't mean, however, that you do nothing or give up.
Focus on the process of education: ask him about what he enjoys about writing; finds difficult; the surprises he learns about himself when writing; etc. In other words, take the focus off of grades and put on engagement.
In a situation like this, teachers can be of quite a bit of help. Ask teachers (especially favored ones) to encourage him. Hard to hear, but their encouragement will get more results now than yours. At same time, keep the Big Picture in mind; best that he is passionate about something. So, while holding the line on the academic engagement, be sure to support the passion. Be patient, as there won't be huge changes overnight.
Our 12-year-old granddaughter, whom we adopted as a small child, is taking money. She says she is not, but it has been missing from my purse and some cans of change. I have confronted her before. She said she wouldn't take any more. But, again, tonight, she had unexplained money. I do not know how to deal with it.
In part, this is another kind of phase thing. Many (but not all) kids experiment with stealing at around 5 or 6, again at 8, again at 12, and again at 14 or 15. Treat it as an experiment on her part, one that you hope she decides to stop after a few faulty attempts.
Keep confronting her, even if you don't have proof. A parent's intuition is enough, so make use of it. She needs to know that you're noticing.
And when you catch her, have consequences -- not extreme, but enough to get her attention. For instance, paying the money back with interest or working off the debt in the home.
In part, it's an adoption test, too. At different times in their lives, many adopted kids put their adopted parents through the wringer. Essentially, they are testing your love for them. If they break all the rules, will you still love them and still keep them a part of your family?
This is why when you confront her and give her consequences, make sure you also stay connected. This is as deep as it gets, so keep this in mind as the backdrop to the drama currently playing out in your home.