The small molecule DYRK1A inhibitor, harmine, induces human beta cell proliferation, expands beta cell mass, enhances expression of beta cell phenotypic genes, and improves human beta cell function i n vitro and in vivo . It is unknown whether the "pro-differentiation effect" is a DYRK1A inhibitor class-wide effect. Here we compare multiple commonly studied DYRK1A inhibitors. Harmine, 2-2c and 5-IT increase expression of PDX1, MAFA, NKX6.1, SLC2A2, PCSK1, MAFB, SIX2, SLC2A2, SLC30A8, ENTPD3 in normal and T2D human islets. Unexpectedly, GNF4877, CC-401, INDY, CC-401 and Leucettine fail to induce expression of these essential beta cell molecules. Remarkably, the pro-differentiation effect is independent of DYRK1A inhibition: although silencing DYRK1A induces human beta cell proliferation, it has no effect on differentiation; conversely, harmine treatment enhances beta cell differentiation in DYRK1A-silenced islets. A careful screen of multiple DYRK1A inhibitor kinase candidate targets was unable to identify pro-differentiation pathways. Overall, harmine, 2-2c and 5-IT are unique among DYRK1A inhibitors in their ability to enhance both beta cell proliferation and differentiation. While beta cell proliferation is mediated by DYRK1A inhibition, the pro-differentiation effects of harmine, 2-2c and 5-IT are distinct, and unexplained in mechanistic terms. These considerations have important implications for DYRK1A inhibitor pharmaceutical development.