You'll find a list of IRS business codes here: https://taxmap.irs.gov/taxmap/instr/i1040sc-016.htm
Just pick the code that most closely fits the type of work you did for the school district. The IRS uses these codes for statistical purposes only. The code won't have any effect on your taxes.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
