Hi Cynthia, In answer to your question, I start or finish each class with a multiplication or a division problem, and I assign 2 or 3 problems for homework. Students must use clustering of some sort to explain their answers. This has worked well because we slid into 4 digit numbers multiplied by 3 digit numbers. [The year she was born multiplied by his weight, was our last problem. 1991x113=? ]
I have continued to have them estimate their answer before they solve the problem. Clustering has helped this class understand place value and the magnitude of numbers better than any other class I have had.
I am currently working in the Different Shapes, Equal Pieces book on fractions, so students get work with really big numbers, and little pieces on the same day!