B.C.
Rachael, I feel for you. My #3 son was like yours. He went from A's to D's and F's. He wasn't studying or doing his homework. He was half heartedly doing his school work and not paying attention in class.
I found this out when he brought home his reportcard. I went to having him write down his homework assignments and having the teacher initial his assignments in his note book. Then I met with his teachers and found out what they expected. (One said "don't snore in class"!)
I would set down and read his assignments at home and then asked him the questions at the end of the chapter. My wife worked with him on his math assignments. (She was a math major in college.) When he had assignments, I'd have him give them to me. I'd go over them and tell him which answers were wrong. He made the corrections. Then I'd make sure he had his homework in his backpack for school the next day. When I found out he wasn't turning the assignments in, even though we had them done, I had a cow.
I told him the next time he didn't turn in an assignment I would go to class with him and go to every class. I scheduled a week of my vacation and accompanied him to class. He was so embarrassed to have me with him in class, that before lunch the first day he asked me to come out in the hall and begged me to go home and he would get his homework done and pay attention in class, and all the other things I had been asking him to do. So, I said ok, and went home.
His teachers were amazed at the change in his behavior . . . and his academic progress. I still went over his homework with him and made him sit down and do his writing assignments and reports. We had a couple of all night sessions because he would tell me he was working on it, his assignments, when he was just procrastinating.
I was working 12+ hours a day, then working another 2 to 4 hours a night plus time on the weekends. After I started working with him, I began doing the same with my other kids. As soon as they saw I was prepared to use my vacation and free time to do this they all improved their homework and study habits. They didn't want dad to go to school with them.
How did it turn out? My son went from D's and F's to straight A's. He graduated salutitorian (#2 in his class) and gave a commencement speech. He earned a full ride scholarship for his first four years of college. He graduated from USC medical school last year and became the first doctor in our family. He passed his boards and is now practicing in Northern California.
Was all the crying and whining and fights and losing vacation time worth it? YOU BETCHA ! ! ! I'd do it over again in a heartbeat. He married a very nice lady and has 4 kids. They are very happy. And so am I. Its not easy being a dad sometimes.
Good luck to you and yours.