I suggest you try two kinds of manipulatives for teaching multiplication concepts. Start with a Multiplication Bead Board (you can buy this, or make a notebook version). Work thru a booklet to teach the concept that 3 X 5 = *** *** *** *** *** Multiplication Bead Boards are available thru Montessori supply companies (www.montessorimaterials.org and go to resources. You will find MANY wonderful downloads on this site- all free).
2. Use Decanomial Bead Bars (denominations of 1 - 10) to demonstrate mixed problems in multiplication. You can also see Decanomial Box material at the above link.
Go to on-line albums for instructions on how to use the materials (SHU Chen Jenny Yen, moteaco, Montessori World, etc.)