In the Montessori method we use something we call the long chains and the short chains, they are for squaring, cubing, skip counting, etc.
This type of material would be wonderful for your student, you could make a chain of five using pipe cleaners and beads.
Visit one of the following websites for an image of the short chains I'm talking about. http://www.montessorioutlet.com/product_images/M-028.9hr.jpg
With the chain you start counting beads in the first group (1,2,3,4,5). Then move to the next group and see how many beads are in it (1,2,3,4,5!). Now see how many are there if you count all the beads in the two groups (1,2,3,4,5,6,7,8,9,10!), keep repeating the process until you are done.
Then take it a step further and label the last bead in each group (5,10,15,20,25,etc) and have the child take a look. Then, have the child just count by reading the labels. Then, count without the labels but count by fives.
You can also, once he understands skip counting by 5, start doing multiplication (5 taken 2 times is 10, and show the two groups of 5 add up to 10).
You can take the short chain (which has 25 beads) and bend them into a zigzag pattern to create a square. 5 squared is 25!