A graphing calculator is probably the most expensive school supply (besides a laptop) that you will ever have to purchase for a high school student. These calculators are typically required for higher-level mathematics classes such as Trigonometry, Analytical Geometry, Pre-Calculus, and Calculus. Prices start at about $45 and can go as high as $300.
Although other companies have been getting in on the market, there are three main brands of graphing calculators: Casio, Hewlett-Packard, and Texas Instruments. For a student in high school, all three of these companies make calculators that perform all of the functions necessary for a student to pass their coursework. In general, you want to make sure that your student’s graphing calculator is easy to figure out and use on his or her own (many teachers will teach students how to use their calculator, but like any technology, controls that are intuitive will be the easiest for your child to remember how to use), and is permitted on standardized tests (this will rule out many of the QWERTY style keyboard calculators/mini-computers).
Casio makes a number of good, user-friendly graphing calculators in its GSX and FSX series. Full disclosure: Casio is my favorite brand of graphing calculator; I used an FSX through my high school Pre-Calculus and Calculus class and my first year of college Calculus, and I later upgraded to a GSX model for my Differential Equations class. I still use one for my engineering work today. Casio graphing calculators have a graphical screen which allows the user to switch modes (basic computation, matrices, functions, etc.) very easily. Without any outside instruction, most high school students familiar with operating their cell phone can pick up a Casio calculator and make it graph simple trig equations or multiply two matrices. GSX models now come with a full color screen; not a necessary feature but a nice one when graphing multiple functions on the same screen. The best part for parents is that Casio is a relatively cheap brand; prices start at $45 and top out at about $85 for the full-color models.
Hewlett-Packard originally started designing graphing calculators for engineering professionals rather than the student market. Hence, while their calculators are often the most highly praised among people working in technical fields, they are often very hard to learn how to use on one’s own. In addition, they are often the most expensive, with prices starting at around $145 and quickly reaching over $400. For students who are willing to take time and read the instruction manual and are probably going to major in a math or hard science field in college, these calculators can be very good investments.
Odds are, though, your child’s teacher has specifically requested a Texas Instrument calculator. Texas Instruments began marketing graphing calculators to high school teachers soon after introducing their TI-81 and TI-82 models for less than $100 in the early and mid 1990s. As part of their marketing materials, teachers are given free calculators in exchange for turning in proofs-of-purchase from their student’s calculators as well as free teaching materials to train students how to use their brand of calculator. The company has also invested a lot into marketing to the high school students. TI models come in a variety of colors, and the company holds an annual contest for students to develop applications for the calculators (most of these are games). The TI-82 will usually cost about $85 and can get your child through most of the coursework required for Pre-Calculus and Calculus on the high school level. Students taking AP Statistics (or a similar class) will need to buy a TI-83 or TI-85 (prices start at $105) for the advanced statistics functions. It is recommended that any student who wants to major in a hard science or math get a TI-85 for the increased memory and function library. Models TI_86 and higher are generally not allowed on many standardized tests due to their increased memory and word-problem solving capability.