A test of the effectiveness of patterning instruction was conducted with 140 first-graders. First, 383 first-graders from 20 classes were screened on a patterning test. The eight in each class who scored worst were given individual 15-minute lessons on patterning or reading or mathematics or social studies three times weekly for a period of 6 1/2 months. Test results for 140 children still available in May showed that the children receiving patterning instruction were generally superior on a patterning test. They also scored significantly higher on the Woodcock-Johnson (W-J) III Mathematics Concepts Scale 18A than children who received mathematics, reading, or social studies lessons. On the W-J III Mathematics Concepts Scale 18B, children who received either patterning or mathematics instruction scored significantly higher than those who received social studies instruction. There were no significant differences on the W-J III Applied Problems Scale 10, nor on three W-J III reading scales. These results suggest that instruction on understanding patterns can substantially improve 1st-graders' understanding of mathematical concepts. Such outcomes may be specific to the sort of children, primarily minority children from diverse ethnic backgrounds, who were participants in this study. (Contains 3 tables.)