ENTP: SanChlor; ESTP: ChlorSan.
Same temperament combo, so they do look very similar (And that blend is said to be the most rambunctious, since it's both of the "expressive" temperaments; in this case, "extraverted" or "pragmatic"); but "areas of interaction" (Interaction Style, conation style) swapped.
The difference is of course the abstract (conceptual) vs concrete (tangible) focus. Since American (and probably much of the West) society is basically ST, ESTP's will be more about the norm, and they will be more into day to day living, and activity. Like in teens, they will probably be into stuff like partying, and they will often be the life of the party, and help set the definition of "normalcy". They will probably be hard on those seen as "weird". So right there, you can begin to detect the "directiveness" of the S+T preference. They will look fun and sociable, but their attitude will be more "don't call me; I'll call you", as is common for "In Charge" types.
ENTP will be much more conceptually minded, and likely to be "weird", though they will probably still be able to command respect from others, because of their extraversion. They will likely socialize, but not be into as much as the ESTP. The Ne will make them more "light and airy", and accepting of others. In battles, they will probably end up more about "winning" than the ESTP, because of the NT's "structure-focus" in place of the SP's "motive focus".
I imagine both types might be "bad" in class, but the ESTP will be the general noise maker, where the ENTP will be the one who challenges the teacher.