Then, of course, some things can't really be explained adequately at a grammar-school level -- you get kind of an outline of the basics. And that was true even when I was in grammar school, with the old Baltimore Catechisms.
We preach the Word of God directly to little school kids who have no problem understanding it, and also directly to the mentally challenged (Down’s Syndrome for instance). Maybe you should try that instead of all your catechisms