This is an excerpt from my book: Johnson, A. (2016). 10 essential instructional elements for students with reading difficulties: A brain-friendly approach.

Phonemes are the smallest units of sound within spoken words. English has 41-44 phonemes. Phonemic awareness is the ability to notice, think about, and work with the individual sounds in spoken words. Phonemic awareness is one part of the whole literacy learning system. But not all children benefit from phonemic awareness activities. The rule of thumb is that phonemic awareness activities should generally be discontinued once children are reading comfortably at the 1st-grade level. Some students with severe reading difficulties in later grades benefit from having phonemic awareness activities that are part of their total reading program.