The Interval Cards provide extra reinforcement in reading 2nds and 3rds on the staff for: Preschoolers; Students with special needs; Review for any student. These cards can be used as a supplement to any method. There are 48 purple cards with a large-sized staff, including: 2nds, 3rds, Quarter Notes, Half Notes. All cards begin on the Landmark Notes of Treble G and Bass C.There are 48 green cards with a medium-sized staff. They are duplicates of the purple cards, in a smaller staff size