We finish the Sunday school year with a congregational picnic following a Sunday-school-led worship service (end of June to coincide with the end of the Canadian school year).  All of the hymns, readings, prayers, etc. are ones we used in Sunday school that year.  We try and have at least one thing from every rotation.  The message portion of the service connects directly to one of the lessons used, frequently a dramatic presentation of some sort.  When possible, leadership for the service comes from our Sunday school kids.  We have a couple of weeks of Sunday school where our focus with the older children is planning the service, which also serves as a review of the different rotations we did over the year.  They tell us which stories and/or lessons were most important/memorable for them and we go from there.  When the weather cooperates, we hold the service outside.