Psychiatric boarding occurs when patients needing intensive psychiatric services who are already under clinical supervision experience delays in their admission to psychiatric facilities. Initial reports have suggested that the US had a psychiatric boarding crisis during the COVID-19 pandemic; however, little is known about the consequences of this crisis for publicly insured youths. To estimate pandemic-associated changes in psychiatric boarding rates and discharge modalities for people aged 4 to 20 years who accessed psychiatric emergency services (PES) through a mobile crisis team (MCT) evaluation and were covered by Medicaid or health safety net programs. This retrospective cross-sectional study used data from the MCT encounters of a multichannel PES program in Massachusetts. A total of 7625 MCT-initiated PES encounters with publicly insured youths who lived in Massachusetts between January 1, 2018, and August 31, 2021, were assessed. Encounter-level outcomes (psychiatric boarding status, repeat visits, and discharge disposition) during a prepandemic period (January 1, 2018, to March 9, 2020) were compared with outcomes during a pandemic period (March 10, 2020, to August 31, 2021). Descriptive statistics and multivariate regression analysis were used. Among 7625 MCT-initiated PES encounters, the mean (SD) age of publicly insured youths was 13.6 (3.7) years; most youths identified as male (3656 [47.9%]), were of Black race (2725 [35.7%]) or Hispanic ethnicity (2708 [35.5%]), and spoke English (6941 [91.0%]). During the pandemic period, the mean monthly boarding encounter rate was 25.3 percentage points higher than the prepandemic period. After adjustment for covariates, the odds of an encounter resulting in boarding doubled during the pandemic (adjusted odds ratio [AOR], 2.03; 95% CI, 1.82-2.26; P < .001), and boarding youths were 64% less likely to be discharged to inpatient psychiatric care (AOR, 0.36; 95% CI, 0.31-0.43; P < .001). Publicly insured youths who boarded during the pandemic had significantly higher rates of 30-day readmissions (incidence rate ratio, 2.17; 95% CI, 1.88-2.50; P < .001). Boarding encounters during the pandemic were significantly less likely to end in discharge to inpatient psychiatric units (AOR, 0.36; 95% CI, 0.31-0.43; P < .001) or community-based acute treatment facilities (AOR, 0.70; 95% CI, 0.55-0.90; P = .005). In this cross-sectional study, publicly insured youths were more likely to experience psychiatric boarding during the COVID-19 pandemic and, if boarding, were less likely to transfer to a 24-hour level of care. These findings suggest that psychiatric service programs for youths were not prepared to support the levels of acuity and demand that emerged from the pandemic.