The National Association of Rocketry which supports model rocketry clubs and such has a tiered certification for High Power Rocketry (HPR) which is where you get into building very large models and packing your own motors. These certifications involve the usual written exam, but you also have to design a rocket in your target class- and get the design reviewed, and then build it- and get the build reviewed for safety, and then fly it. Since it's more than a book -> test certification and involves an actual hands-on engineering project, I'd consider it a fun one.

https://www.nar.org/high-power-rocketry-certifications/