In this circumstance if it is a school aircraft that you are renting then it is really up to them. It should be detailed in either their Flying Order Book or Ops Manual. If one of these states that the school require you to complete a x-channel dual checkout before you can complete it solo then you have to and the flight is PU/T. Whether you agree with their thinking is irrelevant if its their aircraft you are renting its up to them to set the requirements for using it.