Hi Melanie,

My first thought for an octagonal prism was a stop sign. You might not see this as a prism, but it is. A stop sign is about 2 feet across (your son could measure one) and maybe 1/8 of an inch thick (he could measure the thickness also). Not the greatest example, I agree.

Then I thought, we have received questions in the past from people constructing something that is an octagonal prism. Go to the Quandaries and Queries page on Math Central and use the Quick Search with the term octagon real life. One of the questions returned is about an octagonal birdhouse. The shape of the birdhouse without the roof is an octagonal prism. A second concerns an octagonal room. The room from floor to ceiling is an octagonal prism. If the octagonal base doesn't have to be regular then the top of the poker table that Robert is building is an octagonal prism. Unfortunately none of these has a photograph.

A cardboard box and a 2 by 4 are rectangular prisms. A child's block is a square prism.

I hope this helps,
Penny