Harry's Classes at Hogwarts
Harry has had varying degrees of success in his courses at Hogwarts. Some he likes, some he hates. Some he'd probably like more if the teacher were different. Here's a look with special emphasis on Harry's OWLS exams for his future career as an Auror.
This is a fairly straightforward class that Harry doesn't seem to have immense trouble in. The class occurs in the evenings and is taught by Professor Sinistra. Harry thought he did alright on the written portion of the exam for OWLS. The written chart in the second half of the exam did not go well as Umbridge went after Hagrid half-way through the exam, far below the Astronomy tower. Harry only managed to get about two thirds of the exam finished, thus only getting an "A" on his OWL.
Care of Magical Creatures
Care of Magical Creatures involves not only taking care of creatures but learning everything about them. Hagrid has taught this course from 1993 onward. Hagrid's teaching started off with a bang when he introduced the class to Hippogriffs. This course is required for all wizards and witches, but isn't necessary for the Auror job. Harry probably threw everything into the OWLS for this class so as to support Hagrid. For this effort, he got an "E", but decided to drop the class anyway.
Charms class is about learning spells that usually focus on making on object do something unusual. One of the first things the students do in that class is try to make a feather levitate. Harry seems to generally do well in this class, and is usually at an "acceptable" or "exceeds expectations" level grade wise. This is another course that is recommended for the career path of an Auror. Harry managed to get an "E", allowing him to continue his path to being an Auror.
Defense Against the Dark Arts
DADA is probably the class Harry has had the most success in. For one thing, a lot of what he's learned has come in good use during all his many adventures. Each year of DADA has had a different teacher, and only one of them could truly be trusted in the end (Lupin). When Harry starts Dumbledore's Army, he uses a lot of things he learned in the various DADA classes to teach the others. Harry believes he did very well for the OWLs, and even produced a Patronum for bonus points. Harry received an "O" (the best possible grade) in this class.
Divination is, in the trio's words, a joke. Divination is especially annoying for Harry because Professor Trelawney is usually predicting Harry's upcoming death. Still, he and Ron have a good time now and then making up homework answers. Hermione was in the class with them originally, but left when she got fed up with it. Harry and Ron, however, kept pressing on with the class. Harry and Ron both failed their OWLs in this class, so they have since dropped it.
This is a class that Harry personally excels at. It's difficult to say whether it's really a class or not since it's only been shown in the books once. Perhaps it's just an introductory thing, and once students are secure enough with flying they no longer have to attend. Either way, Harry learned his first day that he is an excellent flyer, and it has since become one of his favorite things to do.
Herbology is concerned with various plants that are used in mainly in potions. Harry seems to get along well with the teacher, Professor Sprout. In fact, he believes he did fairly well in the OWLs for this particular course. His work paid off as he got an "E" in this class.
History of Magic
History of Magic is a snore for almost everyone in the class, except maybe Hermione. The teacher is a ghost who apparently forgot to take his body with him to class one day. Harry and Ron often turn to Hermione for help in this class. They would do better if they could manage to stay awake. It was during the OWLS for this class that Harry fell asleep and dreamed that Sirius had been captured by Voldemort. Because of this, Harry failed to get an OWL in this class.
Potions would probably be a different story if it weren't for Professor Snape. It seems that Snape has a "tiny" grudge against the Potter family in general because of the humiliation he endured from James Potter. As such, he's done his best to make this class a living hell for Harry. This is one of the classes Harry needs if he wants to become an Auror. He didn't think he did so well during the OWLs, however. He managed to get an "E", leading him to believe he wouldn't be able to take the next level of Potions (Snape demanded nothing less then an "O"). However, when a new teacher replaced Snape in Potions, Harry was able to take this class.
Transfiguration is no easy task for any wizard or witch. Transfiguration involves transforming something into another thing. For example, on the first day of class their job was to transform a toothpick into a needle. The class is taught by Professor McGonagall who is also the Head of Gryffindor House. Unlike Snape with the Slytherins, she expresses little favoritism if any towards the Gryffindors. Transfiguration is also a class needed to become an Auror. Fortunately, Harry received an "E" in this OWL, thus allowing him to continue the course.