We tested a specific theoretical assumption of a learning trajectories (LTs) approach to curriculum and teaching in the domain of early length measurement. Participating kindergartners (n = 189) were assigned to one of three conditions: LT, reverse-order (REV), or business-as-usual (BAU). LT and REV students received one-on-one instruction using the same activities from a length LT, while the REV condition reversed the LT order. At posttest, LT and REV children exhibited significantly greater learning relative to BAU peers. But importantly, LT children outperformed their REV peers. We conclude that instruction following LTs (i.e., providing instruction just beyond a child's present level of thinking, progressing through the levels in order as the child advances) may promote more learning than an equivalent amount of instruction using the same activities but that are not theoretically sequenced.