For the MYP program, the IB never measures the rigor of the program, even if you follow it through to year 10. They measure whether or not the teachers are applying the criteria correctly with the assignments that have been sent in. Although you would think that this would automatically mean that there would be rigor, it can be quite the opposite.
In other words, as long as the assignments done in gr 10 give the kids the opportunity to reach the highest level on the chart, IB will be happy, it doesn't mean that any of the students actually get to that level. Like I said, it is a wonderful program when done correctly, but if it is only being done in gr 6-8 I would be very skeptical. In fact, I'm not sure that the IB organization will actually approve a program that doesn't go all 5 years. If you want to know more, you could ask the district to see their plan that has to be approved and accepted by the IBO before a school can start using the IB name. It is also a very expensive program, so I can't imagine that the district has that kind of money to spend if they are not going to be in compliance with the IB program.