Obviously the type and level of involvement in curriculum design depends on the age and interests of the students. I have been a secondary school teacher for the last 30 years in schools that have a high proportion of troubled and disengaged students and surprisingly it is these types of students that often benefit most from being involved in their own curriculum planning.
In a nutshell, what I have found is this:
Better performing students have less interest in being involved in curriculum planning. They are certain of their educational goals and are willing to trust their curriculum to those that regard as experts.
On the other hand, poorer performing or disengaged students benefit from being involved in determining their own curriculum. They benefit most from this because they do not intrinsically trust or value the curriculum chosen by those they regard as authority figures (since they regard themselves as failures anyway). My best experiences with these students are through negotiationof contexts fro learning that they consider valuable to them.
At this educational level the curriculum is guided by relatively broad statements of content. As an example, one broad curriculum statement at year 8 level is "Energy appears in different forms including movement (kinetic energy), heat and potential energy, and causes change within systems (ACSSU155)" , thus students can be involved in selecting a suitable context for learning that interests them while still meeting the intent of the curriculum.
My guiding principle is to negotiate curriculum with these students that:
1. is most like the expected curriculum, or
2. has some connection with the expected curriculum, or
3. leads to knowledge not unlike the intended curriculum, or as a last resort,
4. benefits the student in some general educational way eg building literacy, numeracy or even just improving their acceptance of the learning process.
Student engagement in curriculum design has been for me a psychological tool to improve engagement of disengaged students. IN general, already engaged students do not seem to need or even want to be involved very much.