How do I convince my students to sign up for both AP Physics C mechanics and E&M?

On the "Pretty Good Physics" teacher message board - yes, sorry, you must be a teacher to join - a teacher asked how to approach the new signup process for AP exams.  Starting in 2019-20, students must sign up by November (for a full-year course) in order to take the exam.  It's February now, so I know this seems out of date. I think it's worth thinking about now that the October panic of "aargh, should I sign up or not!!!?!" has subsided.

A teacher teaches both AP Physics C mechanics AND E&M.  Completion of the exam is required in order for her students to earn a GPA boost on their transcript.  "Because of the cost," in the past she's allowed students to take either or both exams - even though she covered material and assigned work for both tests in the spring.  But back then, students could decide last-minute whether to pay and sit for the exams.

This year, this teacher worried.  Since students had to register by November... what if they are too scared to sign up for E&M, even if she knows they'll do well?  Even worse, what if the students conspire - "let's sign up for only mechanics, 'cause then we can make teacher skip E&M entirely because none of us signed up!"

She said she needs a plan of what to say to convince students to sign up for E&M - something that's not just "E&M is good for you, it was my favorite course, it'll be yours, too!"

The correspondent is so right, that students are generally risk-averse.  Suggestions about what the teacher personally likes, or what is good for the students, tend to fall on deaf ears - as she suspects.

For those who are teaching APC as a second-year course, I'd suggest following this sequence, teaching algebra-based E&M first, proceeding to calculus-based mechanics, and finishing with calculus-based E&M.  That will start removing the fear of a subject students haven't even seen.  And, this will allay the particular worry that students might try to emotionally blackmail the teacher into not teaching E&M with the whine, "but no one signed up for it!"

I don't like using transactional reasoning, but here it will likely be effective - "We're doing E&M regardless of what you sign up for, so you're being evaluated on that material anyway.  You can only get the GPA and transcript bonus if you sign up.  And I expect that you will do well."  After all, to me the fundamental reason to teach AP is to give students an initial transactional reason to engage.  By the end of the course, they develop a love for physics, an understanding of physics as an end in itself rather than a means to an end.  Yet AP gives us cover while we build expectations and skills in a difficult course - bear with me, because you'll get an extra 0.5 on your GPA and boost your chances of getting into the special college that lets your parents brag to their friends.

Finally, as to the cost of the exam... what do credit hours at a university cost, even a public university?  More than the $94 that an AP exam costs.  Much, much more.  The cost argument is a straw-person.  I mean, obviously it's foolhardy for students to waste money on an exam they won't pass, but isn't the whole point of our teaching to boost the probability that they will pass?  Isn't it the student's job to work hard to make sure they can pass?  If most of the class is failing - which, I must emphatically point out, was NOT the case for this particular correspondent - then something systemic is wrong with the teacher, the students, or the school structure that set everyone up for failure.

There is one possible loophole you might use... Mechanics and E&M are separate courses.  The College Board requires sign-up for full-year and fall-semester courses by November.  However, if your school lists E&M as a second-semester-only course - as on a block schedule - then the sign-up deadline is later.  Talk to your AP coordinator and school registrar if you need to try this.

Most likely, your students will grumble and complain about the early sign-up.  Then they'll just sign up for both exams.  Then they'll be that much more focused on learning all of the content, knowing they're locked in to both exams, that they don't have an out in the spring of their senior year.  Then they'll do well, earn college credit, and be grateful they didn't wimp out.  Sure, there might be a couple of students who don't pass the E&M exam; but they will be far outweighed by those who appreciate your dedication to them, your caring preparation for their college physics weed-out class that they'd otherwise take in a 300-person impersonal lecture hall.