An 'in progress' Workbook is one that includes lessons that have not been assigned a due date (in a date format Workbook) or to a unit (in a unit/subject format workbook). These lessons are referred to as 'unscheduled' lessons. An 'in progress' Workbook is visible to students, but they won't see the unscheduled lessons until you have assigned them a due date or placed them in a unit.