Speaking from experience, It is normal to freeze up.
When I first started as a rookie. I froze and would just stare until my partner would take control and order me to do something.
I think that was due to lack of experience on my part. Since I started as a brand new EMT with no field experience I wasn't used to these type of situation. Even though I knew what to do I would just freeze up cause I would freak out.
Practice and More practice will make it perfect. Give them alot of scenarios (hands on, not on paper) to work with.
Terry