As a consultant to several scool districts, and a retired teacher of 35 years, I find that probabiity can be included in the math curriculum from grade one. The children can relate to the chance of getting a color of block or a kind of sucker from a bag. They can collect data from samples and make predictions based upon their samples. The kinds of samples can become more involved as the students move through the grades. In the school districts that I have worked with we have included probability from grade one on in the curriculum. The teacher, in following the curriculum needs to be responsibly for selecting the appropriate materials to use in teaching the concepts. The Investigations program is not a curriculum and therefore will not match up with a given school districts curriculum. Often times we will need to supplement the Investigations materials in order to meet the desired understandings of a curriculum at a given grade level.