As I see you are working with Middle school boys they are such a fickle age group. The attention span is sometimes limited. If they are not engaged with the concept of the project they like to hurry and move on, with little care to craftsmanship or quality.
Many times they do not know what to do. Many times they have not been given extensive background in materials or selection of subject so they struggle moving from one thing to another. Many times the projects are not challenging enough to hold their interest.
So since you just have boys a curriculum full of construction type art: clay, cardboard, printmaking, drawing cartoon/cars/machines, perspective one point/two point/three point. Many of these projects will be more long term vs. short term projects requiring focus on planning, collaboration, construction. Guide the boys with essential questions: What kind of paint job would you design for your first car? What would a machine look like if morphed with an animal? What would your extreme make over bedroom look like as a perspective drawing and as a cardboard model? What kind of design would you put on a skateboard/snowboard that guys your age would buy? What would the storyboard of a video game you would create look like?
This might cause your boys to pause, and think and focus.