I have been using NCSS in my high school class room for 22 years. I find it very easy to use and my students use it to calculate their results for their lab reports, science fair projects, and now they are using it for AP Research projects. It can be used for everything from the basics to the most advanced statistics. NCSS is very affordable for any high school budget.
As Statistician teaching statistics in the University, I have to say that NCSS is the tool that I have used since 1997. With all the procedures that you need for research or to make a good, informative presentation, it can be used for teaching in a university. Here in Idesem-Chile we have found it to be the best tool to support our measurement activities. I recommend this tool to make your job more enjoyable!