Groups of 10 might be too large. It'll be easy for some students in the groups to not participate. You might want to try smaller groups, such as six.
It is a good idea to assign a group leader, but equally important is to assign roles for the other students. That way everyone feels like they are contributing. You can decide the other roles depending on the activity. For example, there could be a person who takes notes, someone in charge of the time, another person in charge of asking you questions, etc.