A reinforced wallboard core is prepared from a slurry comprising a mixture of .beta.-calcium sulfate hemihydrate, a cellulose ether additive other than CMC and an amount of water that is sufficient to form a slurry and resulting in a wallboard density of less than 0.8 g/cc. The .beta.-calcium sulfate hemihydrate is hydrated by the water forming a wallboard core reinforced by the cellulose ether additive. The cellulose ether, having a molecular weight of at least about 20,000 and a viscosity grade of at least about 100 cps, is selected to give the reinforced wallboard core improved nail pull resistance and greater flexural strength than unreinforced wallboard of the same density. The reinforced wallboard core may be used for reduced-paper wallboard and/or for lightweight wallboard, for example.