Martin, Joanne - I Can Read Music, Volume 1 - Cello - Alfred Music Publishing

Joanne Martin's "I Can Read Music" Books are perfect for creating a strong foundation for sight reading. It is thorough. It is well graduated so the skills of looking ahead, seeing patterns, playing without stopping, and recognizing notes and rhythms are never difficult yet get stronger over time.
I use it for all my students. I highly recommend it.