FWIW, last year, my son knew about the May 20 deadline for the MPE, and with all of the things @rvhappynow mentions above with end of year craziness plus he had an internship in engineering that he worked 15 hours a week, it slipped his mind and he ended up taking it cold. One the deadline date. Managed to score fine so while he would have done better if he had studied/practice tests, he was not in any jeopardy. If your kid is a good math student, I bet they will be fine, especially if he gets the chance to study/practice some.
One other thing. During our group advising session at NSC, the advisor said that they could take the MPE exam again. Of course, he still had not studied/practiced because no one knew this would be offered, so he just kept the score he had.
So, at this juncture, he has only one attempt to take it before May 20. If he doesn’t get the score he wants/needs, have him practice it more before his NSC and they may offer the MPE again. Or heck, just take it again anyway after May 20 and see what happens. The worse they can say is it won’t count.
Good Luck! Let us know how it works out.