As an SLP who treats babies with feeding challenges, I frequently hear from parents how excited they are to begin teaching their baby to use a sippy cup. Problem is, those sippy cups seem to linger through preschool.
Parents often view it as a developmental milestone, when in fact it was invented simply to keep the floor clean and was never designed for developing oral motor skills. Sippy cups were invented for parents, not for kids. The next transition from breast and/or bottle is to learn to drink from an open cup held by an adult in order to limit spills or to learn to drink from a straw cup.
Once a child transitions to a cup with a straw, I suggest cutting down the straw so that the child can just get his lips around it, but can’t anchor his tongue underneath it. That’s my issue with the sippy-cup: It continues to promote the anterior-posterior movement of the tongue, characteristic of a suckle-like pattern that infants use for breast or bottle feeding. Sippy cups limit the child’s ability to develop a more mature swallowing pattern, especially with continued use after the first year. The spout blocks the tongue tip from rising up to the alveolar ridge just above the front teeth and forces the child to continue to push his tongue forward and back as he sucks on the spout to extract the juice.
Discontinue use of the sippy cup if the child is over 10 months. Allow your child to develop the next milestone by mastering a mature swallow pattern. That is, unless you want to go to an orthodontist and speech language pathologist!