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.
I have used several statistics tools, but NCSS is the best statistics tool. It is easy to use because the interface and menu are easy to be used. And NCSS is very useful to support an analysis [in] data research.