This is a response to the additional information part of the SMU supplement on the CommonApp. maximum 500 characters.
^Are you assuming that we know what the essay prompt is? Because we do not.
If this is just an additional information essay, I personally do not see the purpose of what you have provided. There is no requirement to further convince them that you want to study hard, because if the Uni believes that you are a worthy applicant, they will bear that assumption in mind that you will be focused in your academics.
The additional information essay, is typically, to inform the University about something that perhaps they would not have otherwise known from your application. Perhaps, you took a gap year, or graduated early, or somethine along those lines. It is not really an opportunity to sell yourself as much as it is to just inform them about something that they may need to know.