I think your response was perfect. Having been exposed to a topic, or even working within a topic for a while does not imply that all learing pertaining to the topic has been completed. The purpose of spiraling curricula speaks to the need for students to be given many opportunities to explore a topic as they move along a developmental continuum. Having taught Investigations at grades 3, 4 and 5 I've had to meet this challenge myself many, many times. But I have found that both within the program, and on my own, I have been able to provide these kind of students/parents with appropriately challenging learning opportunities, while keeping within the topic being covered. I would say to hold your ground! The richness of mathematics isn't in the completing of assigned problems. It is found in the spaces between them. good luck.