Sand is silicon dioxide. Of course it is a compound. The difference between the answers may be due to confusion, also. PURE sand is SiO2 and that's a compound no matter how you slice it. If you pick sand up from the beach, along with a few golf balls from a nearby golf course, a few rings that are lost, some mud and trash washed up from the an ocean or the Gulf, etc. then that IMPURE sand is a mixture. You can see why its a mixture. The confusion part, is that those people who say it is a mixture are thinking of impure sand, not pure sand. I hope this helps. I can make a mixture of PURE table salt, throwing it on the floor and sweeping it up with a broom. The dirt I pick up from the floor makes it a mixture but the PURE salt is still NaCl and that's a compound.
