There are couple of differences between scholastic and adult tournaments.
One, scholastic tournaments are using shorter time control. Many of them finish in one afternoon. Most adult tournaments are lasting for days, except the club tournaments.
Two, scholastic tournaments are giving trophies, while adult tournaments are giving prize money.
Third, adult tournaments attract more people from other areas. Some might fly over to play.
Four, scholastic tournaments do not allow parents to watch. At adult tournaments, anyone can watch games.
Overall, adult tournaments are much more serious than scholastic tournaments because of the involvement of money.