In Reception, one of most vital jobs is to ensure children can hear, say and read sounds. We tend to focus on the 'pure' letter sounds as opposed to the letter name because this helps children to segment and blend the sounds to read words. 

For example, a = ah, not ay and s = ssss, not suh. In Read Write Inc, we talk about bouncy (short, sharp sounds eg b) and stretchy sounds (elongated eg l) and the children are encouraged to spend time practising their pronunciation. If you want to help at home,  here's a quick video detailing the correct pronunciation for all 44 sounds in the English language: