In the travlos (1999) study, more practice led to poorer retention and transfer test performance than less practice. a possible explanation for this result is that:

There are many variables that affect both retention of skill and the ability to transfer it; such variables are the frequency of practice blocks, amount of practice, homogeneity of tasks etc. It is important to distinguish between ability to perform and ability to teach. While ability to perform goes up, it is probably that at some point, certain parts of the motor skill become automated; the recnstruction process is not needed anymore and the reflex is automatic. Due to this, an individual might have high ability to perform, while low ability to teach. When there are only a few repetitions, automations have not set in yet and the experimental subject is conscious of the whole process; he has to mentally reconstruct it and thus it is easier for him to transfer his knowledge to another.