Final answer:
Jack could not remember that Abraham Lincoln was the 16th president because he never encoded the information during his social studies class.
Step-by-step explanation:
In 9-year-old Jack's social studies class, he didn't remember that Abraham Lincoln was the 16th president because he never encoded the information in the first place. Encoding is the crucial first step in creating a new memory, involving the processing of information so that it can be stored. Just as an e-reader can't display a book you haven't downloaded, the brain can't recall information that it hasn't encoded.
Without effortful encoding, which requires attention to the details and active engagement with the information, Jack cannot retrieve and recall the fact about Abraham Lincoln when he needs it. This concept can be compared to how most Americans can't recall specific details of a penny's design because those details were never encoded into their memory.