Despite a vast amount of research, debate continues concerning the mechanisms underlying correct use of morphological systems such as the English past tense. Relatively little is known about precisely what, when, and how children acquire aspects of inflectional morphology due to the paucity of studies examining the earliest stages of development, and the generally narrow focus on a small number of items and predictors. To address these problems, we provide comprehensive evidence concerning the earliest stages of development. 543 English-speaking children (196 2-year-olds, 176 3-year-olds, 171 4-year-olds) took part in a past tense elicitation task. Responses were elicited for 300 verbs (200 for 2-yr-olds) and measures derived (largely from child-directed-speech) for a wide range of frequency, phonological and semantic predictor variables. We present the outcomes of analyses relating these novel predictor variables to the unique behavioural dataset, revealing the cognitive and linguistic underpinnings of children’s early past tense development.