The ability to explain the occurrence of errors in children's speech is an essential component of successful theories of language acquisition. The present study tested some generativist and constructivist predictions about error on the questions produced by ten English-learning children between 2 and 5 years of age. The analyses demonstrated that, as predicted by some generativist theories [e.g. Santelmann, L., Berk, S., Austin, J., Somashekar, S. & Lust. B. (2002). "Continuity and development in the acquisition of inversion in yes/no questions: dissociating movement and inflection," "Journal of Child Language," 29, 813-842], questions with auxiliary DO attracted higher error rates than those with modal auxiliaries. However, in wh-questions, questions with modals and DO attracted equally high error rates, and these findings could not be explained in terms of problems forming questions with why or negated auxiliaries. It was concluded that the data might be better explained in terms of a constructivist account that suggests that entrenched item-based constructions may be protected from error in children's speech, and that errors occur when children resort to other operations to produce questions [e.g. Dabrowska, E. (2000). "From formula to schema: the acquisition of English questions." "Cognitive Linguistics," 11, 83-102; Rowland, C. F. & Pine, J. M. (2000). "Subject-auxiliary inversion errors and wh-question acquisition: What children do know?" "Journal of Child Language," 27, 157-181; Tomasello, M. (2003). "Constructing a language: A usage-based theory of language acquisition." Cambridge, MA: Harvard University Press]. However, further work on constructivist theory development is required to allow researchers to make predictions about the nature of these operations.