Mileage for what? You cannot claim the mileage from your home to a school (or school to home) --that is commuting which you cannot use. If you drive between schools during the school day, you can use that mileage on a Schedule C as a business expense.
Will the school district be giving you a 1099Misc instead of a W-2? If so, you are indeed an independent contractor.
https://ttlc.intuit.com/questions/2893577-does-a-1099-misc-mean-i-m-self-employed
https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax
https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs
https://ttlc.intuit.com/questions/2903027-how-do-i-report-income-from-self-employment
https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct
It's unusual for a substitute teacher to be an "independent contractor". Regular W-2 employees may not deduct job expenses, at all . (Teachers are allowed an up to $250 above the line deduction for classroom supplies).
As the other answer indicates, commuting is not deductible regardless of employee/contractor status.
@Hal_Al Agreed it is unusual for a substitute teacher to be an independent contractor and receive a 1099Misc but I have seen it happen with small private schools, for example, that are not part of a larger school district. Of course, if there is one school, then there would be no need to drive between locations during the school day. There are scenarios where a sub might need to travel from one school to another for mornings, afternoons, etc. that would be an example of something the OP could use mileage for on a schedule C. But not commuting from home to school or back home, as he/she may have been led to believe.