Background: DFCI ALL Consortium Protocol 11-001 assessed the efficacy and toxicity of Calaspargase pegol (SC-PEG), a novel pegylated asparaginase (ASP) formulation with longer half-life, compared with standard pegaspargase (SS-PEG). Methods: Patients (pts) aged 1-21 years with newly diagnosed acute lymphoblastic leukemia (ALL) or lymphoblastic lymphoma (LL) were eligible. At study entry, pts were randomly assigned to receive either intravenous SS-PEG or SC-PEG, 2500 IU/m2/dose. Pts received 1 dose during the first treatment month. Beginning week 7, SS-PEG was administered every 2 weeks for 15 doses, SC-PEG every 3 weeks for 10 doses (30 weeks). Serum asparaginase activity (SAA) (considered therapeutic at ≥ 0.1 IU/mL) was assessed 4, 11, 18, and 25 days after the induction dose and before each post-induction dose. End-induction minimal residual disease (MRD) was assessed in ALL pts by IGH/TCR PCR. Results: Between 2012-2015, 239 eligible pts enrolled (230 ALL, 9 LL); 120 assigned to SS-PEG, 119 to SC-PEG. After dose 1, SAA remained ≥ 0.1 IU/mL in ≥ 95% of pts on both arms through day 18. Median SAA was higher (0.319 IU/mL vs 0.056 IU/mL) and more pts had therapeutic SAA (88% vs 17%, p˂0.001) with SC-PEG vs SS-PEG 25 days after dose 1. Post-induction, median nadir SAA (NSAA) were similar ( > 1.0 IU/mL) for both arms. There was no difference in rates of ASP-allergy, pancreatitis, thrombosis, hyperbilirubinemia, osteonecrosis, or infection. Of 230 evaluable pts, 99% of SS-PEG and 95% of SC-PEG pts achieved complete remission (p = 0.12). For B ALL pts, there was no difference in frequency of high end-induction MRD (10.3% SS-PEG, 9.5% SC-PEG, p = 1.0). With 4-year median follow-up, 4-year event-free survival (EFS) (90% confidence interval) for SS-PEG was 90.2% (84.3, 93.9), 87.7% (81.5, 91.9) for SC-PEG (p = 0.78); overall survival (OS) was 95.6% (91.0, 97.9) for SS-PEG, 94.8% (90.0, 97.3) for SC-PEG (p = 0.74). Conclusions: Every 3-week SC-PEG had similar EFS, OS, safety profile, and NSAA compared with every 2-week SS-PEG. The high NSAA observed for both preparations suggest dosing strategies can be further optimized. These data informed FDA approval of SC-PEG for pediatric pts. Clinical trial information: NCT01574274.