Inclusion Criteria:

          -  Patients must be newly diagnosed and have:

               -  Eligibility confirmed by rapid central pathology and molecular screening review
                  on APEC14B1:

                    -  Classical histologic type (non LC/A) WNT medulloblastoma

                    -  Positive nuclear beta-catenin by immunohistochemistry (IHC)

                    -  Positive for CTNNB1 mutation

                    -  Negative for MYC and MYCN by fluorescence in situ hybridization (FISH)

          -  Patient must have negative lumbar cerebrospinal fluid (CSF) cytology

               -  Note: CSF cytology for staging should be performed no sooner than 14 days post
                  operatively to avoid false positive CSF; ideally, CSF should be obtained between
                  day 14 and day 21 to allow for final staging status before enrollment onto the
                  study; patients with positive CSF cytology obtained 0 to 14 days after surgery
                  should have cytology repeated to determine eligibility and final CSF status;
                  patients with negative CSF cytology from lumbar puncture obtained 0 to 14 days
                  after surgery do not need cytology repeated; patients with negative CSF cytology
                  from lumbar puncture obtained prior to surgery do not need cytology repeated
                  post-operatively

          -  Patients must have eligibility confirmed by Rapid Central Imaging Review on APEC14B1;
             patients must have =< 1.5 cm^2 maximal cross-sectional area of residual tumor; whole
             brain magnetic resonance imaging (MRI) with and without gadolinium and spine MRI with
             gadolinium must be performed

          -  Patients must be enrolled, and protocol therapy must be projected to begin, no later
             than 36 days after definitive diagnostic surgery (day 0)

          -  Peripheral absolute neutrophil count (ANC) >= 1000/uL

          -  Platelet count >= 100,000/uL (transfusion independent)

          -  Hemoglobin >= 10.0 g/dL (may receive red blood cell [RBC] transfusions)

          -  Creatinine clearance or radioisotope glomerular filtration rate (GFR) >= 70
             mL/min/1.73 m^2 or a serum creatinine based on age/gender as follows:

               -  3 to < 6 years of age: maximum (max) serum creatinine 0.8 mg/dL (males and
                  females)

               -  6 to < 10 years of age: max serum creatinine 1 mg/dL (males and females)

               -  10 to < 13 years of age: max serum creatinine 1.2 mg/dL (males and females)

               -  13 to < 16 years of age: max serum creatinine 1.5 md/dL (males) and 1.4 md/dL
                  (females)

               -  >= 16 years of age: max serum creatinine 1.7 mg/dL (males) and 1.4 mg/dL
                  (females)

                    -  The threshold creatinine values were derived from the Schwartz formula for
                       estimating GFR utilizing child length and stature data published by the
                       Centers for Disease Control and Prevention (CDC)

          -  Total or direct bilirubin =< 1.5 x upper limit of normal (ULN) for age, and

          -  Serum glutamate pyruvate (SGPT) (alanine aminotransferase [ALT]) =< 135 U/L (3x ULN);
             for the purpose of this study, the ULN for SGPT is 45 U/L

          -  Central nervous system function defined as:

               -  Patients with seizure disorder may be enrolled if on anticonvulsants and well
                  controlled

               -  Patients must not be in status epilepticus, a coma or on assisted ventilation at
                  the time of study enrollment

          -  Patients must have receptive and expressive language skills in English, French, or
             Spanish to complete the QoL and neurocognitive assessments; if a patient meets these
             criteria but the parent/guardian speaks a language other than English, French, or
             Spanish, the patient may still be enrolled and tested, and the parent-report measures
             should be omitted

          -  All patients and/or their parents or legal guardians must sign a written informed
             consent; assent, when appropriate, will be obtained according to institutional
             guidelines

          -  All institutional, Food and Drug Administration (FDA), and National Cancer Institute
             (NCI) requirements for human studies must be met

        Exclusion Criteria:

          -  Patients with metastatic disease by either MRI evaluation (brain and spine) or lumbar
             CSF cytology are not eligible; patients who are unable to undergo a lumbar puncture
             for assessment of CSF cytology are ineligible

          -  Patients must not have received any prior radiation therapy or chemotherapy
             (tumor-directed therapy) other than surgical intervention and/or corticosteroids

          -  Pregnancy and Breast Feeding

               -  Female patients who are pregnant are ineligible due to risks of fetal and
                  teratogenic adverse events as seen in animal/human studies

               -  Lactating females are not eligible unless they have agreed not to breastfeed
                  their infants

               -  Female patients of childbearing potential are not eligible unless a negative
                  pregnancy test result has been obtained

               -  Sexually active patients of reproductive potential are not eligible unless they
                  have agreed to use an effective contraceptive method for the duration of their
                  study participation

          -  Patients with a history of moderate to profound intellectual disability (i.e.,
             intelligence quotient [Q)]=< 55) are not eligible for enrollment; PLEASE NOTE:
             Children with a prior history of attention deficit hyperactivity disorder (ADHD) or a
             specific learning disability (e.g., dyslexia) are eligible for this study