The What Works Clearinghouse reviewed the research on two practices used in center-based settings with 3- to 5-year-old preK children, as well as a number of specific curricula. Positive results are shown for (1) Phonological awareness training and (2) Interactive and dialogic reading.
The earliest clues involve mostly spoken language. The very first clue to a language (and reading) problem may be delayed language. Once the child begins to speak, look for difficulties with rhyming, phonemic awareness, and the ability to read common one-syllable words.