KC Gardens

What raised gardens would be educational for school kids?

I have 2 3'x3' raised planting boxes in an outdoor classroom at an elementary school in Olathe. Do you have any recommendations on what would be educational for the kids? Some of my thoguhts were: butterfly bush, pussy willow or blueberry bush. Looking for something conducive to the learning process. They have 4 lower raised planting boxes for each class to plant flowers or veggies. - Bryan -