There has been research done since 1902 (
here's the link) proving such. Krashen and White confirmed the research in 1991 using modern statistical analysis.
Here's another link (just chapters V and VI) from some 1897 research republished in 1913. This goes way back to prove that direct spelling instruction is a waste of time. We don't learn to spell that way. We learn to spell by doing massive amounts of reading and learning to edit our own writing.