"You start classes on September second."
Translation:Tú empiezas las clases el dos de septiembre.
It is wrong...
The only "ordinal number" (first, second, third, etc.) used in Spanish dates is "Primero".
All other dates use "cardinal numbers" (two, three, four, etc.).
You're trying to literally translate it rather than translating it in the way the Spanish write their dates:
Formula for Saying the Date in Spanish
el + day + de + month (+ de + year)
So, September second=
el dos de septiembre.