First of all, how old are you? Do you have any siblings? What are your family's financial situation?
You need to give your parents a reason to allow you to have a dog. You don't need ways to make them let you have one. Start by showing them how responsible and mature you are. Keep your room clean, your homework done, and just generally stay out of trouble. You might want to volunteer for a chore or two around the house ON A REGULAR BASIS. Like, do the dishes every tuesday and thursday. And start doing your own laundry. Parents love that. Ask your mom for a "laundry day". Mine was Wednesday when I was a kid. Every Wedsday after school, the washer and dryer were mine to use for all my clothes.
Keep this up for a few weeks, and then ask them for a dog in a resonable and nice way. Don't whine or beg. That will just irritate them. Explain how you would take care of the dog, and refer to how responsible you have been lately, and tell them why you want a dog.
I like most cats better than I like most people. I'll try to be nicer if you try to be smarter.
I agree with all the previous suggestions and also think maybe you should volunteer to care for someone else's dog so you can learn what is involved in the way of time and energy. Who would take care of the dog while you are in school? Putting a dog outside in a pen or on a chain is not good animal care. If both your parents work during the day, they are right to think you shouldn't leave a dog home alone for so many hours at a time. I can understand you wanting a dog for company ,especially if you are home alone from the time you get home from school until your parents get home. An adult dog that is already house broken might be a good choice as long as there is a way for it to go outside at least once during the day.
this is the second posting from this op, I replied to the first one but then it disappeared from the site?? Anyway I agree with the other members, you need to show your parents that you are responsible and I definitely think if you can offer to help out say weekends in an animal rescue or get hands on experience with a friends or neighbours dog it will give you an idea of what is involved in the care of a dog and show your parents that you are willing to commit. Think hard and be honest with yourself, because a dog is a long term commitment 10+ years.