Each Tier of work carries teacher guidelines on interactive and hands-on methods of teaching / learning. Group and whole class activities are provided with the manipulatives along with step wise guidelines. It is very easy for teachers to follow and then add ideas of their own.
Thus, children typically cover more in a year than is possible with more passive learning methods in which all children move at the same pace / level.
Instead of preparing worksheets, teachers spend their time on making better plans to meet the individual needs of all children.