Which of the following does NOT fall under the classification of "small grains"?

The classification of "small grains" typically includes cereals that are harvested for their seeds. These grains feature small, edible seeds that are used for food, livestock feed, and various industrial and commercial purposes. Oats, barley, and wheat all fit into this category, as they are indeed small grains commonly grown and utilized for these purposes.

Corn, on the other hand, does not belong to the "small grains" classification. While it is a crucial agricultural crop, it is categorized as a large grain or a cereal grain. The seeds of corn, also known as kernels, grow much larger than the seeds of small grains and are treated and processed differently in agricultural practices. This distinction between the size and type of grain allows for proper classification and understanding of their uses in agriculture. Hence, among the given options, corn is the only one that is not classified as a small grain, making it the correct answer.