Building Stamina in 1st Grade

Building stamina is first grade wasn't as bad as I thought it would be.  It actually took my fourth graders longer than my first graders to build stamina in writing and reading.  My first graders were able to stay in one spot and continuously read and write for 20 minutes.  I actually stopped the timer because I saw some of my students massaging their little hands.    We have two more tasks to go; listening to reading and word work.  I have to admit that I am a bit scared when my students get the chance to pick their activity.  Will there be chaos?  We will soon see!!