A child who reads aloud fluently and cannot say what the passage meant is not unusual. Reading consists of two distinct capacities that develop on separate tracks.
Decoding turns marks into words
The first strand is converting letters into sounds and blending them into words. It is a specific, teachable skill with a defined end point, since eventually it becomes automatic.
Systematic phonics teaching works through the correspondences between letters and sounds in a deliberate order, from the most reliable to the least.
English is comparatively awkward for this because the same letters represent different sounds in different words. That irregularity is why the teaching sequence takes years rather than months.
Comprehension is not a single skill
The second strand is understanding what the decoded words mean together. This depends on vocabulary, sentence structure and, most of all, knowing something about the subject.
A reader who decodes a passage about tides perfectly and knows nothing about tides will understand little of it. The missing element is knowledge, not technique.
This is why comprehension cannot be fully taught as a set of strategies. Practice in finding the main idea does not supply the background a particular text assumes.
The two combine multiplicatively
Reading requires both. Weakness in either produces poor understanding, and strength in one cannot compensate for absence in the other.
Children with strong decoding and weak comprehension are frequently missed, because reading aloud sounds competent and the gap only appears under questioning.
Children with strong comprehension and weak decoding are usually noticed sooner, since the difficulty is audible from the first term.
Automaticity frees capacity
Working out each word consumes attention. While decoding is effortful, little is left for holding the meaning of the sentence, let alone the paragraph.
Once decoding is automatic, that capacity is released for understanding. This is the reason fluency practice continues after a child can technically read every word.
It also explains why a child's comprehension can appear to improve suddenly without any change in teaching. The bottleneck shifted rather than the understanding.
What the home contributes
Conversation and being read to build the vocabulary and background knowledge that comprehension draws on, including for texts a child cannot yet read alone.
Reading aloud above a child's independent level does this efficiently, since the adult handles the decoding and the child receives the language and the content.
Where a child is making little progress with decoding despite consistent teaching, an assessment through the school is the appropriate step rather than more practice at home.