Background: Down syndrome acute lymphoblastic leukemia (DS‐ALL) is characterized by the high frequency of CRLF2‐rearrangements, JAK2-mutations, or RAS-pathway mutations. Intriguingly, JAK2 and RAS mutations are mutually exclusive in leukemic sub‐clones, causing dichotomy in therapeutic target choices. Results: Here we show that in primary leukemic cells from DS‐ALL, in the absence of RAS-mutations, wild-type (wt)RAS is active, and/or can be induced by the physiological ligand TSLP of the transmembrane-receptor CRLF2. We show active/inducible RAS in 14/20 (70%) of primary DS-ALL samples analyzed, 8 of which had no RAS-mutations, but 75% of those had either mutated or hyperphosphorylated JAK2. No wtRAS cases with mutated/hyperphosphorylated JAK2 were observed that lacked activated RAS protein. We prove in a cell model that elevated CRLF2 in combination with constitutionally active JAK2 is sufficient to activate wtRAS. We show that TSLP boosts the direct binding of active PTPN11 to wtRAS. Pre‐inhibition of RAS or PTPN11, but not of PI3K or JAK signaling, prevented TSLP‐induced RAS‐GTP boost. Using multivariate-clustering based on RAS‐activity/inducibility we show significant separation between standard‐risk and high‐risk DS‐ALL groups. Cox proportional-hazards model showed protein-activity (but not mutation status) as independently predictive of outcome. Conclusions: Our data indicate that RAS protein activity levels (and not JAK2/RAS mutation profiles), are predictive of outcome. Importantly, our data suggest that inhibition of RAS and direct RAS‐pathway components should be combined with PI3K/mTOR and/or JAK2 inhibitors for high-risk cases. Therapeutically this is relevant for >75% of DS‐ALL and our additional data suggest that it warrants further investigation in high-risk non‐DS-ALL.