Something that damages productivity is counterproductive.
What would be the word for something harmful to your learning process? For example, teaching you wrong, so that later you must first unlearn the wrong knowledge before you learn it right?
Say, a book for little children contains some words badly misspelled for humorous purposes, but since it's the first contact of the children with these words, they learn them that way, thinking this is the correct spelling, and later they have trouble learning the right spelling at school.