Of all children in the US born with Cerebral Palsy (CP), 30-40% of them will be diagnosed with Hemiplegic CP (HCP), presenting with one side of the body weaker than the other. The resulting asymmetries impede the ability of children with HCP to distribute weight evenly between their lower limbs. This often contributes to poor postural control and 'favoring' of their uninvolved side for stability during balance and gait. Much is still unknown about the biomechanical characteristics of asymmetry in the lower limbs. There are a few previous research studies completed in biomechanics labs that highlight some gaps in knowledge regarding our understanding of posture and balance in this population of children, but the availability of clinical assessments that help inform the implementation and impact of treatment targets for posture and balance are sparse. This dissertation showcases two independent studies aimed at some of the gaps in knowledge for posture and balance in children with HCP. The first study in this dissertation presents and tests the reliability when a clinical measure, the Posture and Postural Ability Scale (PPAS) was modified for use in children with HCP going through a therapeutic process. The PPAS was originally developed and tested with adults in controlled settings, often with individuals being placed in postures for examination. For the study presented here, modifications focused on scoring postures when children with HCP naturally assumed various sitting and standing postures during treatment. Researchers and an experienced therapist video-coded the modified PPAS. Intrarater and interrater reliability was calculated via Cohen's kappa, percent agreement and Intraclass Correlation Coefficients. Although reliability amongst and between researchers were weak (kappas < 0.7), videos were successfully scored, demonstrating the tool is feasible. In addition, some high levels of intrarater reliability was obtained by a more experienced clinician. Suggestive that this modified PPAS could serve as a potential tool for qualified clinicians to collect meaningful posture and postural control data. The second study addressed a specific gap in knowledge about the characteristics of gait anticipation (GA, i.e., expectation of initiating a step) in children with HCP on balance. Balance and limb symmetry metrics were compared during standing in three children with HCP and typically developing (TD) peers that were matched by age and sex, alongside a third (independent) sample of 12 unmatched TD children. Motion capture analysis and force plate technology were utilized to record and follow how center of pressure (COP) and center of mass (COM) move during quiet standing (without anticipating gait) and standing with GA. This study applied a Symmetry Index (SI) to COP displacement and COP velocity allowing for quantification of asymmetries between the lower limbs during standing with and without the anticipation of gait. Children completed multiple standing trials where they were ask to stand for 35 seconds (5 seconds to obtain balance and 30 seconds of data collection). Standing trials, involved sets where children were instructed that they would not walk forward and GA trials where they were asked to stand knowing that a light would indicate they should walk forward. The light also indicated which limb (i.e. right or left) the child should step forward with first. Limb designation for stepping forward was randomly generated. Data was examined across and within (15 second blocks) 30 seconds of standing. We had the following hypotheses: 1) GA would increase COP displacement and COP velocity for children with HCP greater than TD peers who would have no change; 2) children with HCP would have different levels of symmetry between the lower limbs when expecting to walk than TD peers; and 3) children with HCP would have different reaction times based on the limb (i.e., involved versus uninvolved) they were asked to start walking with. The HCP group showed the largest increase in COP displacement when comparing standing with no expectation of walking where they had an average of 22.0 ± 10.0 mm over 30 seconds of standing to an average of 24.5 ±9.90mm during GA. The matched group average was 11.3 ±8.87mm with no expectation of walking and 4.6 ±12.6mm with GA. The TD group's COP displacement remained relatively similar with an average of 8.04 ±6.40mm during when not expecting to walk and an average of 8.29 ±6.70mm with GA. Similar increases were seen for COP velocity. Comparisons for symmetry between limbs showed that COP was displaced more underneath the uninvolved side (first 15s was 79.52%) for children with HCP, and that COP displacement asymmetry switched to become larger underneath the involved side over time (the latter 15s was -82.81%) when there was no expectation for walking. This was inverted during GA, where children with HCP initially had more COP displacement on the involved side (-72.68%) and transitioned to higher levels on the uninvolved side (99.66%) as they prepared for gait initiation. Children with HCP took 0.2 seconds longer to initiate gait with their uninvolved (not preferred) side and also took twice as long to initiate gait overall in comparison to TD peers. Our data suggests that our listed hypotheses may be correct. However, this study has limitations to sample size, demographics and biomechanical metrics. Future studies should replicate these findings and include larger, more diverse samples with further metrics such as load. If findings are confirmed, this data suggests that therapies should consider that children with HCP might change postural strategies during standing when they are anticipating walking forward in comparison to simply standing in place. This dissertation seeks to set a foundation for collaborations between biomechanists and therapists alike, potentially highlighting novel opportunities to develop more innovative treatment options for children with HCP. / Doctor of Philosophy / Children with hemiplegic cerebral palsy (HCP) show limitations in coordination and activation of muscles on one side of their body; additionally, clinicians report an asymmetrical distribution of weight in their legs during standing and walking based on observation. This lower limb asymmetry is often paired with poor coordination and is believed to negatively impact posture and balance. Children with HCP often have difficulty starting and stopping walking, altered balance during sitting and standing, and challenges completing everyday activities such as navigating around or across obstacles and climbing up steps. I have worked together with my committee members to complete two independent projects measuring posture and postural control. The first project is a reliability study where researchers tested the utility of a modified measurement tool that could be used to score postures and postural control of children assuming natural postures during therapy sessions. The modified tool was based on a previously developed tool called the Posture and Postural Ability Scale (PPAS). The study had multiple researchers and a therapist score previously recorded treatment videos. Outcomes suggest that our modified PPAS could be used to score postures from video recordings of therapy session, but that increased modifications in the tool and scoring protocol are needed to improve the reliability of the tool. The second project funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development involved children with HCP and typically developing (TD) peers. The goal of the project was to understand if children with HCP change characteristics of standing when they know they will begin to walk. We also wanted to better understand issues surrounding how symmetrical (or not) children with HCP were with the use of both their involved and uninvolved legs. We found that children with HCP do alter characteristics of standing when they anticipate walking much more that TD peers. We also found asymmetries between the two limbs during standing that differed based on children with HCP's anticipation of walking.