This resource is a fun extension activity for anyone teaching binary code with their students. Binary clocks have been around for awhile and demonstrate a practical application of binary code for students. I used this worksheet with third graders without an issue. I would recommend 3-8th grade for this resource.
Students should have some grasp of counting in binary in order to complete the worksheet. I have been using a wonderful curriculum, CS Unplugged, to teach our third and fourth-grade classes about computer science and introducing them to binary code. CS Unplugged is a great resource. Most, if not all, of my resources, are extensions of CS Unplugged activities and lessons. You can find information here, http://csunplugged.org/. The curriculum is licensed creative commons and is easily adaptable.
There is a key provided. If you enjoy this resource, I have other binary lessons and resources available.