The vast majority of activities students perform in class require some sort of focused effort. In addition, many activities demand attention to detail, creativity, collaboration, and the expense of some cognitive energy.
When designing activities that support greater ownership and internal motivation, keep in mind the risks of rewards. This is not to say that positive feedback is not important (more on that later), but if your plan to encourage ownership and motivation is based on rewards, you will likely fall short and potentially set your students back further from owning their work than when they began. Instead, look for ways to incorporate autonomy, mastery, and purpose into the activity. Make sure the purpose is well understood, provide a clear path from activity to better mastery of the concepts, and give students some choice in how they go about delivering the final product.
For more, check out this video based on Daniel Pink's Drive: The Surprising Truth Behind What Motivates Us.
In addition to the activities you design, the feedback you give also plays a part in supporting ownership and motivation. Feedback to students, both formal and informal, should be given frequently during activities. Not only does feedback help keep students on task, but it also can be a significant factor in helping students take ownership and develop internal motivation. Dr. Heidi Grant Halvorson's blog post, The Feedback You Need to Be Giving provides a wonderful explanation of how different types of feedback affect different people. Essentially, Dr. Halvorson reports that for experts, being more critical in your feedback is useful and motivational. For novices, additional praise is the better motivational feedback. In other words, if you are giving feedback to an expert, telling them how to do better next time is more helpful than piling on the praise. For people just staring out, frequently telling them what they are doing well is more helpful.
There are obvious implications here for giving feedback to students. If you are working with a student who full grasps the concepts and is looking for more of a challenge, feedback that suggests areas for improvement is a good idea. For students unfamiliar with the concepts, begin more positive in your feedback will help them stay motivated to continue trying.
Effective educators support the academic development of their students. The level of "academic maturity" a student has is largely the result of how much she takes ownership of her work and the level of internal motivation she has to do better. Both ownership of work and motivation are topics teachers can support in their classes with some attention to designing appropriate activities and giving appropriate feedback.