Although basing instruction on a learning trajectory (LT) is often recommended, there is little evidence regarding a premise of a LT approach--that to be maximally meaningful, engaging, and effective, instruction is best presented 1 LT level beyond a child's present level of thinking. We evaluated this hypothesis using an empirically validated LT for early arithmetic with 291 kindergartners from four schools in a Mountain West state. Students randomly assigned to the LT condition received one-on-one instruction 1 level above their present level of thinking. Students in the counterfactual condition received 1-on-1 target-level instruction that involved solving story problems three levels above their initial level of thinking (a skip or teach-to-target approach). At posttest, children in the LT condition exhibited significantly greater learning, including target knowledge, than children in the teach-to-target condition, particularly those with low entry knowledge of arithmetic. Child gender and dosage were not significant moderators of the effects.