Objectives Researchers and clinicians specializing in breastfeeding often rely on measuring one nursing session to characterize the breastfeeding relationship. However, less is known about the descriptive or statistically predictive characteristics of one nursing session. The purposes of this study are twofold: (1) to explore the relationships between variables in a single nursing session; and (2) to study the association between variables in a single nursing session and infant length‐for‐age (LAZ) and weight‐for‐age (WAZ). Methods In 63 nursing mother‐infant pairs in the United States, anthropometric measurement and observation of a single nursing session revealed six nursing session variables: fore milk fat percent, hind milk fat percent, infant milk intake, duration of session, time since last session, and time of day of session. Results A principle factor analysis, undertaken to explore latent variables underlying the six session variables, revealed two factors: (1) loaded highly on fore and hind milk fat percentage, reflecting the overall fat percent in a feed; and (2) loaded highly on milk intake and hind milk fat percentage, indicating the process of breast emptying. In multivariate analyses of all session variables on infant LAZ and WAZ, only hind milk fat percentage was significantly negatively associated with LAZ (β = −0.14, P = .01 (two‐tailed), R2 = 0.070), confirmed by a significant negative association between LAZ and factor one (β = −0.32, P = .05 (two‐tailed), R2 = 0.090). Conclusions This research describes the dynamics of a single nursing session, and has the potential to help explain variation in infant growth and nutrition.