Thank you!! I'm not the only one. Another failed attempt by the writers. And I'm basing this off of my knowledge of the education field as well. You need to have some sort of 'credentials' in the field you want to teach, especially if it is a foreign language course. And preferably (based on state) at least a Master's or working towards it if you want to teach high school. PhD is definitely preferred at the college level.
I'm just going to IGNORE all that because that doesn't pertain to how I portray Will anyways. He's taking these night classes to brush up on his Spanish/teaching skills because he hardly using it outside the classroom. So he's trying to make sure that what he's teaching is useful for his students.