Hi,
All samples of chiral compounds (provided you do not have a racemic mixture) rotate plane polarized light. It is not possible to predict by how much and in what direction without testing a compound.
For a pair of diastereomers, they do not have the same relationship as a pair of enantiomers, in that it is impossible to infer the direction and magnitude of one diastereomer's light rotation given the rotation information for another diastereomer.
However, keep in mind that chiral compounds rotate plane polarized light, and enantiomers and diastereomers are words to describe relationships between 2 chiral compounds - this was tough for me to get at first.