Having a dog, especially a young one/puppy is a BIG responsibility. Especially during school. You must walk them every day. Depending on the breed you may have to exercise them longer or they will be a complete handful. If they don't get their exercise they'll have all of that energy balled up and it'll release in bad behavior. If you get a puppy are you ready to train it? Consistently and constantly? Are you ready to clean up every mess he/she makes? All the urine, and fecal matter? What about barf? Are you ready to explain the chewed up clothes, shoes, and furniture to your parents?
During school when you have those semester tests or a big project, will you be committed to your puppy still? Do you think you have enough room for a dog? Do you have enough time all year?
If you get an older puppy are you ready to break all of the bad habits the previous owner ignored? Will you be committed still-- all year, every year until that dog passes away? Are you ready to start paying attention to another life? Are you going to feed him/her twice a day? Play with them? Bathe them? Does your family have enough money for a dog? The vet trips, shots, worming treatments, flea and tick treatments, a bed, food, toys, cleaning sprays, and if you're not able to train them a trainer. Are you ready to groom them? If a long haired breed, every day?
If you get an older dog, what if he has health issues that must be tended to every day or even multiple times a day? What if your dog is loud and you start getting complaints from neighbors?
Are you ready to spay/neuter your dog and care for them while they recover? If you don't you will have a lot of troubles. Males humping, marking and escaping. Females attracting males into your backyard.
There is a LOT to think about when you get a dog. Start researching and making sure you have the time, money, and patience with dealing with a dog.