Is it bought or brought?

How many times have you heard someone say, “I bought my mother to school?" and asked yourself, “Why can't this person understand the simple difference between bought and brought?"

1. Bought is the past time of buy.
   She bought her mother a gift for her birthday.
   We bought a new car last week.
2. Brought is the past tense of bring.
   Last week, my friend brought her puppy to school.
   My father brought home a friend for dinner.
3. The word bring has an r. So the past tense of bring is brought, also with an r.
4. The word buy does not have an r and therefore the past tense too does not have the letter!

Now get cracking on this exercise! Is it bought or brought?