Have I Made Any Progress?

One of my tasks is to make sure that the teachers I teach are using proper grammar in the classroom. It is necessary for them to use proper grammar because they do not teach grammar in the lower grades. The only way the students are going to learn proper grammar at that level is to learn from what the teacher models in the classroom.  It has been a difficult journey. I take sentences I have heard in the classroom (instructions from the teachers) and give them to the teachers to correct. Many are so badly constructed that they cannot figure out what the message was. How on earth can the students understand what is being said if the teachers cannot interpret the meaning?

My latest test in this area was posting a small story on the FB page. I asked for someone to respond with what is wrong with the sentence spoken by the sales clerk. No one has posted. Here is the story:
A woman is shopping for shoes. She is a vegan, so does not like to wear leather things, but will wear cow leather in order to have shoes. What is wrong with the sales clerk's English?
“Deer cannot-ah? How come cow can?”