I don't think a laptop is really necessary in the 9th grade for schoolwork, unless you go to really tech-savvie high school where everything, (and I mean EVERYTHING) is done through computers and the internet.
However, having a laptop is a very convenient luxury at any age, and if you can afford it, then you should get one. As long as your careful, the durability of a MacBook will definitely last you through the end of your college years. That being said, Apple updates the internal technical specs of its line of notebooks every 7 months, and MacBooks basically come with model years just like vehicles do. These upgrades include things such as memory, graphics card, processor, etc, but nothing too major. A complete overhaul of the MacBook happens about every 5 years (ex. the change from the white and black polycarbonate MacBook to the new unibody Aluminum MacBook).
Take this information and judge for yourself, whether you want a MacBook now or later. You'll only have the newest model MacBook for only a few months, at most, but MacBooks are still quality computers that you could certainly rely on. My friend at my college dorm uses his dad's MacBook from maybe 2003 that runs Mac OS X 10.4 Tiger, and it works fine.
Don't worry about software updates for your MacBook. When connected to the internet, the computer will automatically search for updates to your operating system (OS) and any other applications that you may have such as Microsoft Word, iTunes, etc. Therefore, you may not have the most powerful MacBook, but your software is completely up-to-date.
Oh yeah... Apple >>>>>>>>>> Microsoft.