By the time students are at the end of a project timeline, their work should have been evaluated so often that there are simply no mistakes.  How?  Through frequent and thorough feedback and revision processes, formative assessments, and constant monitoring by the teacher through rubric evaluations, contract meetings, and other intentional review processes designed to embrace the kaizen mindset and give students opportunities to fix their work all along the way.  Summative assessment?  By the end of the project, everyone should get them all right.