Assembling the planters is an exciting time for the students. It is very important that the students are shown how to properly use a hot glue gun. This will help avoid an injuries. Teacher might also consider using low temperature glue guns.
I have found that the best way for students to assemble the planters was one step at a time. I discuss this with the students. I ask them "Now that we have the parts cut out and ready to go, what do we put together first." I let them discuss this and make a list of steps. Then as a class we compare their lists and I ask them what do they build on a house first. I then ask them to look at the planter and their list and see if that is where they started. The class then works together to list the order of steps to assemble the planter.
As the students assembled the planters, I only get out the parts needed for the step we are working on for that day. This helps keep all of the students on the same page. The students who finish first can help the students who are having problems.