Hi. My approach has been the following:
First, I teach Adobe Photoshop to high schoolers grades 10-12.
I introduce the tools and menus i want for them to learn (skills) and then I may show them an example either i have created, or another class form previous years have. I do that, so they can get the idea of "If they did it-then I can do it too!) problem i have found with this approach is the designs i get very close resembles what they "saw" versus what they found on their own.
I try to give them days if not a whole week for them to finish one project:
Day 1 Lesson intro and materials
Day 2-4 Students work on their projects (All while being ok to talk to others in a relaxed classroom setting, sharing ideas and tips on Photoshop)
Day 5 Turn in their work in google-classroom and the following Monday we discuss our project, answer a few questions related to the Project and critic each others work.
I learned Photoshop pretty much on my own. I want my students to have the same experience, but with "some" guidance from me obviously; as an instructor. If you're interested on what my students learn thru PBL practices, I invite you to see our Lessons online at: www.photoshopskillz.blogspot.com