OG is excellent for decoding, but there are other programs that help take a student to the next level in fluency, once they've completed OG, such as Read Naturally. Comprehension is yet another level, usually helped most by learning active reading strategies--so more cognitive and executive functioning strategies than anything else. Comprehension also naturally improves as decoding becomes automatic, because this frees up cognitive and EF functions for comprehending, rather than decoding. Some active reading strategies include KWL (know-want to know-learned) and SQ3R (Survey-Question-Read-Retell-Review).
