It is extremely difficult to know where to start with a third grade student who has some splinter skills.  If the third graders are frequently using the wrong consonant sounds (except for b and d confusion that can be handled separately), they need to start at the Beginning Green Level.  Also, students who move very slowly, such as cognitively impaired pupils, should start with the Green. Likewise, students whose speech and language problems make them very difficult to understand, should use the Green.  On the other hand, students who struggle mostly with the vowel sounds and the general inconsistencies of English phonics, can start at the Overlapping Strategy materials (see that link).  This approach requires students to know consonant sounds and shapes consistently and know a few sight words.  It also moves faster than the Green Level.  If you need more advice, call us.