A portion-controlled dispensing straw assembly includes inner and outer telescoping tubes. The outer tube has an upper edge and a lower edge, and the inner tube has an upper edge, a lower edge and an interior chamber for receiving a substance to be dispensed. A seal is disposed within and attached to the outer tube, below the inner tube, for preventing the substance from exiting the interior chamber in a substance-retaining condition. A cap has a lower edge resting on the upper edge of the inner tube in the substance-retaining condition. The cap, upon being depressed, pushes the inner tube within the outer tube to break the seal and allow the substance received in the interior chamber to fall out of the tubes in a substance-releasing condition. The cap, upon being removed, also opens a passage allowing the tubes to be used as a straw.