According to the Association of Waldorf Schools of North America:
Children who transfer out of a Waldorf school into a public [state] school during the earlier grades probably have to upgrade their reading ability and to approach the science lessons differently. Science in a Waldorf school emphasizes the observation of natural phenomena rather than the formulation of abstract concepts and laws. On the other hand, the Waldorf transferees are usually well prepared for social studies, practical and artistic activities, and mathematics.
Children moving during the middle grades should experience no problems. In fact, in most cases, transferring students of this age-group find themselves ahead of their classmates. The departing Waldorf student is likely to take along into the new school a distinguishing individual strength, personal confidence, and love of learning.
and about children transferring into Waldorf schools from state-run schools:
Children who transfer to a Waldorf school in the first four grades usually are up to grade in reading, math, and basic academic skills. However, they usually have much to learn in bodily coordination skills, posture, artistic and social activities, cursive handwriting, and listening skills. Listening well is particularly important since most of the curricular content is presented orally in the classroom by the teacher. The human relationship between the child and the teacher is the basis for healthy learning, for the acquiring of understanding and knowledge rather than just information. Children who are used to learning from computers and other electronic media will have to adjust.
A government study of English Waldorf schools showed that Waldorf pupils' reading skills tend to lag behind state-educated pupils in the first few grades, but that by 5th grade (11 years of age) the Waldorf pupils have caught up and thereafter are ahead of children of the same age who are educated in state schools. Waldorf schools maintain that the literacy-building techniques Waldorf schools use during early childhood—storytelling, music and singing, games, speech, and movement exercises—help to nourish imagination and a love of language which will be carried long after the child learns to read. It is worth noting that Finland, which sends its children to school at a comparable or later age, is one of the most literate societies in the world. Research by Piaget and others also supports the view that early academic learning actually interferes with the development in early childhood of faculties that will enhance later learning capacity.