The Student Background survey administered along with achievement tests in studies of the International Association for the Evaluation of Educational Achievement includes scales of student motivation, competence, and attitudes toward mathematics and science. The scales consist of positively- and negatively keyed items. The current research examined the factorial structure of the 18-item motivational scales in fourth-grade mathematics in the 2011 Trends in International Mathematics and Science Study (TIMSS). Survey data from six European countries were analyzed. In comparisons of alternative models, the fit was adequate when three correlated factors were specified and negative keying was taken into account as a latent factor, or with correlated uniquenesses among negatively keyed items. Participants reading achievement scores correlated systematically to negative keying with coefficients ranging from .254 to .395 in the six samples. Unlike their higher-scoring peers, fourth-graders with lower reading achievement responded differentially to similar items depending on the direction of item keying, in such a way that their motivation scores were biased downward. Implications about the use of reverse keying in surveys for young students are discussed.