These are what I recommend. There is more than one, because what I would recommend is different depending on what you need it for. If you have one of these calculators (or two), I will teach you how to use it in class. If you have a different calculator, you will have to look up how to use it yourself.
While it can stretch to get you through Algebra 2, it is best for Pre-Algebra, Algebra 1 and Geometry.
What are in advanced menus of the TI-34 are front and center here. Solve triangles and use e and log more easily.
Matrices, vectors, complex numbers, combinatorics, numerical approximations, etc.
Can do everything the others do and more, plus graphing. More expensive than the others put together too. Slightly clunky interface, jack of all trades.
This is the $10 calculator I used from middle school to grad school. Never needed a graphing calculator. So I just got by with this little scientific calculator for everything.
I do not recommend this calculator, but I will always have a spot in my heart for this one. But it goes to show you, you can really make anything work even if it's not luxurious. It just forces you to develop other skills too.
Here is what I recommend for each class. The first option is a scientific calculator - the one that is best suited for that class. After that, the TI-84 or other scientitic calculators that would work are also listed, thought they may be less than ideal.
For a typical course on statistics (which also includes a section on probability), there are functions of the TI-84 which the other calculators just don't have.
While most calculators are sufficient, they are all idiosyncratic and each have their own set of limitations and ways of doing things. I like to choose the calculator my students use in each course because I don't want to spend time discussing the differences between different students' calculators. Also, I can easily post videos of just one model for everyone to use as a reference on how to do something (which is especially useful if I have to miss a school day). Going with a different calculator means you will have to look up how it works yourself.
Mainly, I recommend Texas Instruments calculators because they are (1) common, (2) intuitive, (3) use a consistent design language throughout their product line and (4) there are learning materials which incorporate them. I'm not a fan of their 'monopoly' so-to-speak, and I am always happy to check out innovations in the school calculator space. But unless you are into math and calculators and want to pick your own poison, then I will have you all use the same Texas Instruments calculator as a class. It simply, still, is just easier that way.
When two calculators are both capable of doing the same things, what makes one more suited for earlier math courses and the other better for later math courses is usually which buttons and functions are accessible from the main buttons rather than being found deep within sub-menus.
I do not recommend the "he/she will grow into it" approach! For scientific calculators, these are not expensive. (These cost half the price of a popular game on STEAM.) A student looking at the buttons of a calculator and not recognizing most symbols or never using them anyway is sabotaging them. It's like giving them a cheat sheet for the vocab quiz which is the entire dictionary. Too much stuff you aren't looking for getting in the way of what you are looking for - all the time. The calculator buttons should be useful and intelligible to you in the context of your class.
Graphing calculators are powerful, have more features and visualize for you. They are usually allowed in testing environments. They are allowed for most standardized tests. Since they are so helpful, then why wouldn't you want to know how to use it fully for an high stakes test? To not use it would be to put yourself at a disadvantage.
There are drawbacks, however. Just like any calculator introduced too early, before basic skills are developed, can rob you of the need to learn to do things without a calculator, so graphing calculators can prevent important skills from developing in the first place. I have had a student fall in love with an advanced calculator in Calculus class because it could do everything for him and help him "see" the functions. But in college, he was not allowed to use graphing calculators on tests and found he was far behind his peers in being able to visualize these functions in his head. His own skills had atrophied due to over reliance on the calculator too early in his learning.
It's great to have a graphing calculator and use them when you know how to do something laborious, you just don't want to this time. It's useful to practice using it so you know what it can do when you're taking a standardized test that allows it. But I prefer students work without them, especially when they are learning things for the first time. Your PC and phone are better able to generate graphs and animations for you and can solve problems for you if you need to check your work. They just aren't allowed on tests.
However, there are several Statistics functions the TI-84 has that none of the other calculators listed here have. The questions I ask on my tests in Statistics (at least, for now) require beig able to use some sort of calculator. So the TI-84 is required for Statistics, but that is the only course I require it in. However, I will permit students to take Statistics without the TI-84 with special permission if they have strong math skills and they request it.