Once upon a time, a parent brought her 3-year-old child to a child psychologist claiming that her son was gifted.
Mom demonstrated this by whipping out some cards with words on them for the child to read. As expected, the child got every word correct.
The psychologist said, "How interesting! Would you go over to the television set over there and read the words above the knobs?"
The child looked at the words on the television, got scared, and ran away.
He didn't understand words after all. He was decoding.
He wasn't seeing a sequence of letters, associating them with sounds, and stringing them together to form words. He was seeing the visual shape of a word, like "blue," and associating it with the word "blue," which he knew made mom happy.
When kids are put under pressure to learn anything beyond their understanding, they'll use every trick possible to make it look like they learned it.
We see this a lot with young competition students. They will play a Chopin waltz beautifully, but on closer examination, have no idea how to read music. Because the music hasn't been learned and understood. It's been drilled in.
The same is true of any skill, but especially languages.
When kids decode, they might have a product today, but it's tenuous. Worse yet, they won't be able to produce for life.
When kids take the time to understand and learn how to learn, they produce forever.