The present study aimed to extend understanding of preschoolers' early spelling using the Vygotskian ("Mind in society: the development of higher psychological processes," Cambridge, Harvard University Press, 1978) paradigm of child development. We assessed the contribution of maternal spelling support in predicting children's word spelling level beyond the contribution of three internal child measures: early literacy (phonological awareness and letter naming), private speech while spelling (self-directed talk), and behavioral regulation. Children's private speech during spelling--their tool to regulate thinking--has not yet been studied in the early literacy context. Fifty Israeli preschoolers (M = 68.66 months) of middle-high SES were videotaped while spelling words with their mothers and while spelling these words independently. Children's phonological awareness, letter naming, and behavioral regulation were assessed individually. Results showed that children's internal measures (early literacy, private speech while spelling, and behavioral regulation) predicted children's early spelling (63% of the variance), and the external measure of maternal spelling support added uniquely (12%), together explaining 75% of the variance in children's spelling level. Findings suggested that mothers adjust their spelling support to meet young children's existing literacy skills but also coach children to strive toward higher spelling performance. Furthermore, the study illuminates the role of a new measure in the context of children's early literacy-private speech during spelling.