ST Math students continue on to the next concept regardless of how they scored on the post-quiz. Post-quizzes are designed to measure how well students can answer your typical test questions and are not presented with the visual elements used elsewhere in the games.
Post-Quizzes are provided to help instructors measure growth and help teachers identify students who have strong conceptual models but are failing to link the model to symbolic math, as well as to help students develop strong meta-cognition skills.
Most levels in ST Math are generated semi-randomly and are free-response, so it is difficult for students to memorize or guess their way through the games. If a student has passed all of the levels in an objective, then they probably have a good understanding of the math concept visually.
If one or more students have done poorly in an objective, it can help to take them (individually, or in a small group) into their history or in to play as a teacher, and ask them to teach how to play some of the games from that objective. Ask the student to write out the puzzle using symbolic math. This can help the instructor identify the disconnect, and help the student complete their understanding. You can also use assignments if they need further practice.