I use Mr. Andersen's videos all the time in my AP Biology class as a precursor to my lectures. This is my write-a-long, or WAL as I call them, for his "Chi Squared Test" video.
The WAL has students follow Mr. Andersen and are guided to write down importation information as he describes the Chi Squared equation and important terminology (like "null hypothesis"). I have the students pause the video shortly after he describes what a null hypothesis is to read a summary of the information, worded in a way that might be more understandable to some students. Students continue the video and write out two problems with Mr. Andersen.
At the end of the video and the WAL, they are given data from an animal behavior experiment (wet/dry environments and bugs) and have to calculate the Chi Square value. The answer to the problem is not given- you discuss the work and the answer with the students the next time you see them.
Please note that there is no key included with this product. It's good for you to watch the video so you know what your students will see, anyway :)