Researchers in the last 2 decades have highlighted how intervention early in life leads to improved outcomes for children with autism spectrum disorder and other neurodevelopmental disorders. Monitoring biomarkers are assessed serially over time and can be used to provide evidence of an intervention effect. A key feature of monitoring biomarkers is the focus on change. For a recent study, the researcher evaluated white matter neurodevelopment as a monitoring biomarker for the early treatment of neurodevelopmental disorders. Fragile X syndrome (FXS) and autism spectrum disorder (ASD) as used as examples. White matter has unique neurobiology, including a prolonged period of dynamic development. This developmental pattern may make white matter especially responsive to treatment. White matter develops aberrantly in children with ASD and FXS. Histologic outlines in rodents have provided targets for FXS pharmacological intervention. However, pharmaceutical clinical trials in humans failed to garner positive clinical results. The researchers argued that the use of neurobiological monitoring biomarkers may overcome some of these limitations, as they are objective, not susceptible to placebo effects, and are dimensional in nature. As the field moves towards earlier detection and early intervention for neurodevelopmental disorders, scientists are encouraged to consider the advantages of using neurobiological features as monitoring biomarkers.