Reduced soybean [Glycine max (L.) Merr.] yield has resulted from the colonization and feeding of the soybean aphid Aphis glycines Matsumura (Hemiptera: Aphididae). The soybean aphid is able to colonize in the thousands on a single plant leading to soybean stunting, reduced pod set, leaf deformation, flaccidity, as well as the transmission of several plant viruses. Known to be resistant soybean lines to the soybean aphid have been backcrossed with commercial cultivars. Field screening of several soybean lines within each backcross preceded field trials with a single backcross from Jackson, Palmetto, Dowling, and an accession from Shandong province of northern China. Each line was used to test survivorship and fecundity of individually caged aphids. Resistance was evaluated during the V2, R1, R3, and R6 stages of plant development. Fifty replications per resistant line and per plant stage were tested and measured against the susceptible control Harovinton. A t-test was conducted to determine if there are significant differences between the resistant and susceptible cultivars at each plant stage. It was expected that resistant lines would show a significant increase in aphid mortality and a decrease in aphid fecundity in each of the plant stages. The purpose of this research was to determine if resistance is affected during periods of developmental plant growth.