Project Special Elementary Education for the Disadvantaged (SEED) is a nationwide program in which professional mathematicians and scientists from universities and research corporations teach conceptually oriented mathematics to full-sized classes of disadvantaged elementary school students as a supplement to their regular mathematics instruction. Instruction is through a Socratic group discovery format. In the Dallas (Texas) schools, Project SEED was used with all grade levels in schools with a high percentage of low-income students. Evaluation considered program impact after one, two, and three semesters of instruction for four groups of students in grades 4, 5, and 6, 1,666 in all, which were more than 95 percent Black, and more than 80 percent eligible for free or reduced-price lunches. Achievement was determined with the Iowa Test of Basic Skills and some other measures. Impact was apparent with even one semester of SEED instruction, as well as cumulative with two and three semesters. Achievement continued higher for SEED students in comparison with non-SEED students even two years after SEED instruction. Student attitudes toward SEED instruction were positive. Three tables present study findings. (SLD)