Even if students know and understand the different letters and their sounds, they may still have trouble sounding out words. The solution to the problem is to bring in another sense. For example, we teach students to link speech sounds to how they feel when they are pronounced. That way, when they have trouble sounding out a word, they can rely on their sense of feeling to help them read. It's the same principle behind counting beans to learn basic math or doing experiments to understand science.
Some students have trouble remembering words from one day to the next.
They have to sound out each word and often read very slowly. Their spelling skills are weak. These students can't remember the visual patterns of words.