Teen Einstein has created an app for the California Grade Eight Math on Statistics and Probability. Although there are two versions of the app, I downloaded the free app to check out. When you look at the index page, you see there is a practice section with basic and advanced, a quiz page with basic and advanced and the dashboard.
It turns out this app is a sampler so you know the types of questions before you buy the paid app. It has only 5 questions for the basic and 5 questions for the advanced.
So for both the practice and the quiz sections, there are 5 questions and that is all. When you get to the 5th question it asks if you want to buy the full app. The quiz asks the same 5 questions and scores you on your answers. I admit, I had high hopes for this one but I am not going to use it in class. The 5 questions for each section are good but I'd prefer it if there were a few more questions available so I can use it with my students and get a decent feedback.