No its not. I haven't seen a single school in 10 years that uses Dell in any of the cities I've lived in or visited. Its always been Apple, HP, or occasionally I've seen Compaq. I'm sure there are schools that do use them but, they are not a standard, that is just ludicrous.
Dell is shoddy anyway.
We used Dells and HPs at my schools, and I've never seen anything else. God, those things were stuffty.
In highschool, everyone was given a portable HP. After 3 years, my CPU had a constant running temperature of 150C, the battery lasted 2 mins fully charged (I'm not even kidding) and the screen had been replaced once. And I had 3 chargers in 3 years...