Boldface the due date so they are sure to see it.

The two and three-year-olds, who come at nine o’clock, arrive be-leggined and be-muffled, and the teachers have become adept at manipulating zippers.

Wild wheat is small and hard, quite capable of looking after itself, but its heads contain only a few small kernels. Cultivated wheat has lost its hardiness and its self-reliance, but its heads are filled with large kernels which feed the nation.

Thus, you could tell them to look at three o'clock, or look just off-center toward nine o'clock, and so forth. Alternatively, in some microscopes a thin black line appears to cut across the field of view