Before joining the academy in 2013, Professor Simmons was a partner with the Rapid City Law firm of Gunderson, Palmer, Nelson & Ashmore, LLP, where he was a practicing trust and estates lawyer. Prior to his legal career, he was a public school teacher.

Simmons teaches courses in estates, equity, and legal ethics. Although his scholarship ranges from zombie law to Martian law, it focuses primarily on estate planning, the federal estate and gift tax, and trusts.  He is actively involved in trust law reform and a is fellow of the American College of Trust and Estate Counsel (ACTEC), the American College of Tax Counsel (ACTC), and the American Bar Foundation. He serves on the Governor's Trust Task Force for Trust Administration and the South Dakota Advisory Committee to the U.S. Civil Rights Commission.