Udacity has two free introductory statistics courses that they recommend prior to starting their AI nanodegree program:

Intro to Descriptive Statistics [https://www.udacity.com/course/intro-to-descriptive-statisti...]

Intro to Inferential Statistics [https://www.udacity.com/course/intro-to-inferential-statisti...]

Khan Academy also has very in-depth coverage of statistics, starting from the basics. https://www.khanacademy.org/math/statistics-probability

if you want to focus on Statistical Learning, I can recommend Introduction to Statistical Learning Using R[1] by Prof. Hastie and Tibshirani.

[1]: https://lagunita.stanford.edu/courses/HumanitiesSciences/Sta...

I found the lectures entertaining and the exercises of a much lower quality. Not enough of them, shallow and ambiguously worded.

I got something like 90% on the edx MITx probability course and was barely getting 50% for the above mentioned Stanford stat learning course for the 5 weeks of it I completed. I mention the MIT course, (which I highly recommend fwiw) only to support my view that I don't think my experience is aptitude or workload related. But as ever YMMV.

Not a MOOC, but I loved this: http://www.statsoft.com/Textbook/Basic-Statistics/button/1