Inclusion Criteria:  Age: ≥ 4 years (PeNAT validated in patients 4 to 18 yrs) newly diagnosed or recurrent disease: first diagnosis of ALL (i.e. non-relapsed) in maintenance therapy English, French or Spanish-speaking with an English, French or Spanish-speaking guardian (PeNAT available in these languages) without physical or cognitive impairments that preclude use of the PeNAT planned to receive PO 6-mercaptopurine not planned to receive IV, IM, SC or IT chemotherapy or oral or IV corticosteroids during the 7-day study period