Sparx Science is set up to make it easy to set homework for students on different courses (Combined/Separate) and tiers (Foundation/Higher).
Adjust the Higher and Separate settings for each student in the Student Manager. See Changing homework settings for multiple students student.
Sparx will then automatically:
exclude questions only in the Higher specification for students not set to Higher
exclude questions only in the Separate specification for students not set to Separate
Note: KS3 students also have these settings available in case you assign a GCSE topic to a KS3 class.