The Praxis II high school and middle exams specifically permit you to use a graphing calculator. The online Praxis exam provides an on-screen graphing calculator. Consult your individual exam instructions for the details. Some general info is found here:

For the Praxis II Math exams, the student is expected to use technology (namely, a graphing calculator) appropriately as a tool for problem solving. If you have never used one before, you will be amazed at how powerful a tool these calculators are. For example, they will plot curves, find zeroes, and invert matrices, so you do not need to do these things manually.

The on-screen graphing calculator is very similar to the Texas Instrument 83-84 series, which are commonly used in schools. If you want to practice with a graphing calculator for the exam, or to practice for your teaching, get yourself a Texas Instrument. (I use the 84 Plus.) Sometimes they even can be found used. You can get one here:

The TI series is great, but sometimes you need a little help. You can download the official TI manual from their website, but it is absolutely massive. You can more quickly find what you need from the TI Graphing Calculator for Dummies books, which I have used and are very well written.

I understand that the TI N-Spire and the N-Spire CAS (computer algebra system) are not permissible calculators.

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