The goals of this clinical trial are to identify factors associated with the development of problem behavior in Cornelia de Lange syndrome (CdLS) and to develop an effective behavioral assessment and treatment model for problem behavior in children with CdLS. The hypotheses are as follows: 1. Based on pilot data, the investigators hypothesize that individuals with CdLS will exhibit preferences for auditory stimuli relative to other categories (e.g., visual, tactile) of stimuli. 2. Based on pilot data, the investigators hypothesize that individuals with CdLS will exhibit problem behavior to obtain adult attention or to escape task demands relative to tangible and control conditions, as measured by functional analysis results. 3. Function-based behavioral treatments will reduce problem behavior in individuals with CdLS by 80% or greater relative to baseline rates. 4. Individuals with CdLS and problem behavior will exhibit more impaired communication, demonstrate increased emotion dysregulation, and exhibit more severe symptoms of Autism Spectrum Disorder (ASD) relative to those with CdLS and no problem behavior. Participants in the intervention group (families of children with CdLS and problem behaviors) will be asked to complete study measures and attend 2 full days and one half-day of clinic services at Kennedy Krieger Institute so that the study team can provide assessment and treatment of child problem behaviors, and then train parents to apply the intervention. Participants in the control group (families of children with CdLS and no problem behavior) will be asked to complete study measures once every 3 months for a 2-year period to monitor the children. This study will improve the ability to effectively treat problem behavior is CdLS, as well as identify key variables associated with problem behavior in CdLS which may be examined in future studies and clinical practice to foster early intervention and prevention efforts.