We report the glass-forming regions of the ternary Lu2O3-Al2O3-SiO2 and Sc2O3-Al2O3-SiO2 systems. The density, molar volume, compactness, Vickers hardness, refractive index, as well as the glass transition (T-g) and crystallization temperature are compared for two series of RE-Al-Si-O (RE = La, Y, Lu, Sc) glasses that display a constant molar ratio n(Al)/n(Si) = 1.00, whereas n(RE)/n(Si) is equal to either 0.62 or 0.94. Several glass properties scale roughly linearly with the cation field strength (CFS) of the rare-earth (RE3+) ion, except for the Tg values of the Sc-bearing glasses that are significantly lower than expected. Magic-angle spinning Si-29 and Al-27 nuclear magnetic resonance (NMR) reveal enhanced network disorder and increased relative populations of AlO5 and AlO6 polyhedra in the aluminosilicate glasses for increasing RE3+ CFS, but overall similar Si and Al local environments (chemical shifts and quadrupolar couplings) in all samples associated with a constant n(RE)/n(Si) ratio, except for unexpectedly shielded Si-29 NMR signals observed from the Sc-Al-Si-O glasses.