An enduring question of Caenorhabditis elegans development is how multiple Notch interactions specify distinct cell fates at different times and places. Good et al. (p. 1967) have identified two T-box transcription factors – TBX-37 and TBX-38 – that affect the outcomes of two sequential Notch signalling events during early development. ABa and ABp are initially equivalent sister cells at the four-cell stage. The researchers showed that the ability of ABa to give rise to mesodermal precursors relies on its expression of tbx-37 and tbx-38. In response to the first Notch signal, tbx-37 and tbx-38 expression is blocked in ABp and its descendents, preventing ABp from producing mesodermal precursors. A second Notch signal at the 12-cell stage acts in concert with TBX-37 and TBX-38 to promote mesodermal fates in ABa descendents. The authors conclude that T-box proteins modulate crucial Notch interactions during mesoderm development.