Manipulatives That Make Sense Unifix letter cubes are one of the most highly effective manipulatives used to teach kids critical reading skills. The durable plastic cubes are easy to connect and yet they stay connected. The cubes are color-coded to distinguish between vowels and consonants. The set comes with 360 Unifix cubes plus a Phonics Activities Guide and teaching notes. The cubes are housed in a sturdy storage box. Appropriate for Grades 1-3