This paper summarizes the results of research conducted by the National Highway Traffic Safety Administration (NHTSA) to determine how changing vehicle design parameters influence child restraint performance. Initial research consisted of surveying late-model vehicles' interior design characteristics as they pertain to child restraint systems. The next step involved dynamic evaluation of booster seats with respect to injury/excursion criteria measured on child test dummies under conditions which illustrated the changing vehicle design characteristics. Belt-positioning booster seat tests were conducted to evaluate the effect of belt type (lap/shoulder belt vs lap only belt) on seat performance. Differences in small-shield booster behavior when used with lap only belt or laplshoulder belt combinations were established in another series of tests. Another study demonstrated how varying seat back rigidity changed small-shield booster test results.