In order to put something in our short-term memory we listen to it or say it 10 times in 10 minutes or just long enough for it to become a part of our short-term memory but in high school we listen to the same songs every day over the span of years which firmly sets them in our long-term memories. We said or hear the liturgy only once a week but it's part of our long-term memory because we've said it once a week for 15 years or so. I've heard people complain that it's terrible that kids learn the same Bible stories in Sunday School year after year but that's how they become fixed in our memories. The stories with which we aren't familiar are the ones we only heard once in a while; short-term memory.
According to Brain Rules, that's how memory works. So... in confirmation, Sunday School, or even worship, what's the best way to get scripture into long-term memory? It's repetition over time. The key being over time. That doesn't mean it should be repeated 25 times in 10 minutes. It should be repeated 25 times over 10 days, 10 months, or 10 years. The longer it is repeated, the longer it will stay in long-term memory. We may think it's boring for kids but the brain works the way the brain works. There's no arguing with that.