They should be mastering English, band English grammar has identical concepts related to good Spanish. Even if these students are “fluent” which, in most cases the mainstream (ignorant) media probably defines as “communicating well in the language,” their level of Spanish may be horrendous. Thus, if the AP Spanish course is well-taught, it can improve both the student’s Spanish and English skills.
Hit the post button without correcting:
They should be mastering English, AND English grammar has identical concepts....
Seriously, that would probably do them more good than either Spanish or English (assuming they have learned English fluently by this time).
There’s an old line about Heinrich Schliemann, the man who discovered Troy, speaking better Greek than any of the men he hired to help with the dig.
Most illegal Latino immigrants come from poor Mestizo or Uto-Aztecan backgrounds; their families’ grasp of proper Spanish is probably pretty marginal to start.