English vowels are phonologically and orthographically more difficult than consonants when learning to map speech to print. We sought to determine if teaching young at-risk readers and spellers to use a visual vowel hand sign system to segment spoken words into their component phonemes contributed to improved grapheme-phoneme correspondence knowledge, word reading and spelling. Twenty-three at-risk Year 1 participants were assessed prior to receiving Crack the Code--an intervention that incorporates a visual vowel hand sign system for phoneme segmentation--and immediately after its completion on measures of segmentation, grapheme-phoneme correspondence knowledge, word reading accuracy, word reading efficiency and spelling. Analysis of group data showed statistically significant improvement across all measures with effect sizes ranging from 0.73 to 1.83. Explicitly teaching phonemic segmentation with a visual vowel sign system may be an effective way of improving vowel knowledge, word reading and spelling skills of at-risk children.