A lecture about clinical singing. The impact of singing-based intervention on speech fluency across three populations: Major Depressive Disorder (MDD), Parkinson's Disease (PD), and Down Syndrome (DS). Using a pre-post intervention design, we analyzed objective measures (speech rate, pause frequency/duration) and perceptual evaluations from 12 naive judges. Results demonstrated significant improvements: a 218% increase in words-per-minute (p<0.001, d=2.1) and 90.2% reduction in intra-lexical pauses (p<0.01) in DS, with comparable gains in MDD and PD groups. Perceptual evaluations showed 50% improvement in fluency ratings (velocity, rhythm regularity, segmentation) for isolated phrases (ICC=0.78-0.84), with more modest but significant gains in paragraph reading. Notably, comprehension improved only in connected speech (+20%, p=0.014). The intervention's efficacy appears mediated by different mechanisms across conditions - motor planning enhancement in PD, respiratory control in DS, and prosodic modulation in MDD. While single-case limitations apply to the DS cohort, consistent effects across neurological and genetic conditions suggest singing may activate compensatory neural pathways for fluency. These findings support singing as a transdiagnostic tool for speech rehabilitation, warranting controlled trials with larger samples.